Process for the production of a polyester fiber dyeable under normal pressure

ABSTRACT

A fiber consisting essentially of polyethylene terephthalate capable of being dyed under normal pressure and having an initial modulus at 30° C. of about 55 g/d to about 130 g/d, a relationship between a peak temperature [T max  (°C.)] at the peak of a dynamic mechanical loss tangent (tan δ) measured with a frequency of 110 Hz and a peak value of the dynamic mechanical loss tangent [(tan δ) max  ] represented by the formula: 
     
         (tan δ).sub.max ≧1×10.sup.-2 (T.sub.max -105) 
    
     and a (tan δ) max  of about 0.14 to about 0.30 and a dynamic mechanical loss tangent at 220° C. (tan δ 220 ) of at most about 0.055. The fiber is produced by subjecting a polyethylene terephthalate fiber obtained at a spinning speed of at least about 4000 m/min. to heat treatment at a temperature ranging from a temperature at which a dynamic modulus (E&#39;) of the fiber deviates from a tangent line at 180° C. of a logarithm of the E&#39; of the fiber-temperature curve (T min ) plus 10° C. to a temperature of completion of melting (T m3 ) at a melting curve of the fiber measured by a differential scanning calorimeter (DSC) plus 10° C.

This is a division of application Ser. No. 363,628, filed on Mar. 30,1982, now U.S. Pat. No. 4,426,516.

BACKGROUND OF THE INVENTION

The present invention relates to improved polyester fibers includingflat yarns, tows, staple fibers and false twist yarns and a process fortheir production. More particularly, the invention relates to polyesterfibers capable of being dyed with disperse dyes under normal pressure,having excellent color fastness and still having sufficient mechanicalproperties for practical use, and to a process for their production.

Generally polyester fiber, especially polyester fiber consistingessentially of polyethylene terephthalate, has many excellent propertiessuch as tenacity, dimensional stability, thermal resistance and wash andwear property and many varied uses. On the other hand, polyethyleneterephthalate fibers are poor in dyeability and it is thereforenecessary to dye them under the conditions of a high temperature, e.g.,about 130° C., and a high pressure. Consequently, the production of suchfibers suffers from the disadvantages that a special apparatus isrequired for dyeing. Moreover, use of such fibers in admixture withfibers such as wool, acrylic fibers and spandex fibers whose physicalproperties deteriorate upon dyeing under a high pressure and a hightemperature, is limited.

Various improvements in dyeability of polyethylene terephthalate fibersunder normal pressure have been proposed. A process in whichaccelerating agents called as carriers are employed in dyeing, forexample, is known. However, the process has many disadvantages. Morespecifically, such carriers which are irritative and harmful to humanbody worsen working environmental sanitation at a dyeing factory andhave difficulty in disposal of dyeing waste. Further uneven dyeingcalled as a carrier spot may be caused due to insufficiency ofemulsification of the carriers and the carriers may remain in a dyedarticle to deteriorate the color fastness to light of the dyed article.Moreover, the carrier dyeing causes changes in the mechanical propertiesof the polyethylene terephthalate fiber such as a decrease in thetenacity and an increase in the elongation.

A copolymer of polyester with a compound having a metal sulfonate groupor polyether has been considered a polyethylene terephthalate having animproved dyeability. Although such modified polyesters improve thedyeability, it is difficult to polymerize and spin them and the cost ofthe starting materials increases or the excellent mechanical and thermalproperties possessed by polyethylene terephthalate and the colorfastness may deteriorate. Consequently, the improvement in thedyeability resulting from such chemical modification detrimentallyaffects the inherent excellent thermal resistance and mechanicalproperties of polyethylene terephthalate, since the improvement isachieved by introducing a third component which can act as a dyereceptacle for dyeing the polymer.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a polyester fiberconsisting essentially of polyethylene terephthalate having sufficientmechanical and thermal properties for practical use and capable of beingdyed under normal pressure, especially with a disperse dye without usinga carrier.

Another object of the present invention is to provide a process forproducing such a polyester fiber.

Additional objects and advantages of the invention will be set forth inthe description that follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

To achieve the foregoing objects and in accordance with the purpose ofthe invention, as embodied and broadly described herein, the polyesterfiber of the present invention consists essentially of polyethyleneterephthalate capable of being dyed under normal pressure and having aninitial modulus of at 30° C. of about 55 g/d to about 130 g/d, arelationship between a peak temperature [T_(max) (°C.)] at the peak of adynamic mechanical loss tangent (tan δ) measured with a frequency of 110Hz and a peak value of the dynamic mechanical loss tangent [(tanδ)_(max) ] represented by the formula:

    (tan δ).sub.max ≧1×10.sup.-2 (T.sub.max -105)

and a (tan δ)_(max) of about 0.14 to about 0.30 and a dynamic mechanicalloss tangent at 220° C. (tan δ₂₂₀) of at most about 0.055.

Further to achieve the foregoing objects and in accordance with thepurpose of the invention, as embodied and broadly described herein, theprocess of the present invention for producing such a polyester fibercomprises subjecting a polyethylene terephthalate fiber obtained at aspinning speed of at least about 4000 m/min. to heat treatment, at atemperature ranging from a temperature at which a dynamic modulus (E')of the fiber deviates from a tangent line at 180° C. of a logarithm ofthe E' - temperature curve (T_(min)) plus 10° C. to a temperature ofcompletion of melting (T_(m3)) at a melting curve of the fiber measuredby a differential scanning calorimeter (DSC) plus 10° C.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate the invention and, together withthe description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram illustrating one embodiment of an apparatus employedin the process of the present invention, in which the numbered elementsare as follows: 1, extruded filaments; 2, a spinhead with a nozzle; 3, acylindrical heating zone; 4, aspirator; 5, a device for providing anoiling agent; 6, a device for bundling; 7, a take-up roller; 8, a pairof feed rollers; 9, a heater for heat treatment; 10, a pair of deliveryrollers; and 11, a winder.

FIG. 2 is a diagram illustrating another embodiment of an apparatusemployed in the process of this invention where the spinning step andthe heat treatment are continuously carried out, in which the numberedelements 1 to 6 are the same as in FIG. 1 and other numbered elementsare as follows: 7, a pair of take-up rollers; 12, a pair of heatingrollers; and 13 is a winder. In FIGS. 1 and 2 arrows show the directionof running filaments 1.

FIG. 3 is a diagram illustrating a further embodiment of an apparatusemployed in the process of the present invention, in which the numberedelements 1 to 6 are the same as in FIG. 1 and other numbered elementsare as follows: 7, a pair of take-up rollers; 14, a heating cylinder forwet heat treatment; 15, a plurality of slits from which superheatedsteam is jetted into the inside of the heating cylinder; 16, a valve;17, a device for heating steam to give superheated steam; 18, a heater;19, a valve; 20, a boiler; 21, a pair of delivery rollers; and 22, awinder.

FIG. 4 is a diagram illustrating one embodiment of an apparatus for thewet heat treatment of a fiber bundle, a sliver or a tow usingsuperheated steam employed in the present invention, in which thenumbered elements are as follows: 23, a fiber bundle, a sliver or a tow;24, a pair of feed rollers; 25, a guide roller; 26 and 26', slits forpreventing excess leakage of superheated steam within a device for wetheat treatment 27 and controlling the fluctuation of temperaturetherein; 27, a device for wet heat treatment; 28, slits for jettingsuperheated steam provided with the internal wall of the device for wetheat treatment 27; 29, heaters for preventing lowering of thetemperature of superheated steam within the device for wet heattreatment and reducing the distribution of temperature therein; 30, aguide roller; 31, a pair of delivery rollers for the fiber bundle,sliver or tow; 32, a valve; 33, a device for heating steam to givesuperheated steam; 34, a heater; 35, a valve; and 36, a boiler.

FIG. 5 is one embodiment of a false twisting apparatus employed in theproduction of the false twist fiber of this invention, in which thenumbered elements are as follows: 33, a package of fiber; 33, a fiber;34, a first pair of feed rollers; 35, a first heater; 36, a spindle; 37,a pair of feed rollers; 38, a second heater i.e., a stabilizing heater;39, a pair of delivery rollers; 40, a friction roller; and 41, a bobbinfor winding.

FIG. 6 is a graph illustrating the relationship between a spinning speedand a E'₂₂₀ with respect to a fiber before and after the heat treatmentat 245° C. for 1 second at 1% extension, in which a broken line showsthe value of the fiber after the heat treatment and a solid line showsthat before the heat treatment.

FIG. 7 is a graph illustrating the relationship between a spinning speedand a degree of crystallinity with respect to a fiber before and afterthe heat treatment under the same conditions as in FIG. 6, in which abroken line shows the value of the fiber after the heat treatment and asolid line shows that before the heat treatment.

FIG. 8 is a graph illustrating the relationship between a spinning speedand an apparent crystal size at a face of (010) with respect a fiberbefore and after the heat treatment under the same conditions as in FIG.6, in which a broken line shows the value of the fiber after the heattreatment and a solid line shows that before the heat treatment.

FIG. 9 is a graph illustrating the relationship between a spinning speedand a degree of crystal orientation at a face of (010) with respect to afiber before and after the heat treatment under the same conditions asin FIG. 6, in which a broken line shows the value of the fiber after theheat treatment and a solid line shows that before the heat treatment.

FIG. 10 is a diagram for determining T_(min), in which a tangent lineshown as a chain line is drawn at 180° of a log E'-temperature curve anda temperature at which the difference between the tangent line shown asa solid line and the log E'-temperature curve (Δlog E') becomes 0.04 isdesignated T_(min).

FIGS. 11(a) 11(b) are graphs illustrating a dynamic mechanical losstangent(tan δ)-temperature(T) curve and a dynamic modulus(E')-temperature (T) curve, respectively, in which (A) represents afiber of this invention, (B) represents a conventional drawn fiber, (C)represents an undrawn fiber and (D) represents a partially orientedfiber.

FIG. 12 is a graph of one embodiment illustrating a curve of X-raydiffraction intensity of polyethylene terephthalate fiber, in which (e)represents a portion of the X-ray diffraction intensity attributed tothe crystalline region and (f) represents a portion of the X-raydiffraction intensity attributed to the amorphous region.

FIG. 13 is one embodiment of a pattern of interference fringe that wasused to measure a distribution of a refractive index (n.sub.∥ orn.sub.⊥) in the direction of a radius of the cross section of a fiber,in which (g) is a cross section of a fiber and (h) is a pattern of aninterference fringe in which the numbered elements are as follows: 37, afiber; 38, an interference fringe by a medium; and 39, an interferencefringe by a fiber.

FIG. 14 is a diagram illustrating a temperature of completion of melting(T_(m3)) by a differential scanning calorimeter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the presently preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

As a result of a study on the fine structure of polyethyleneterephthalate fibers, it has been found that only a polyethyleneterephthalate fiber having a specific amorphous structure could overcomethe disadvantages of the conventional fibers and that only apolyethylene terephthalate fiber having a specific amorphous structurehas a dyeability under normal pressure and an excellent color fastnessin addition to the suitable inherent properties of polyethyleneterephthalate fibers.

The polyester fiber of this invention consists essentially ofpolyethylene terephthalate and characteristically satisfies thefollowing three conditions:

(I) The initial modulus at 30° C. is about 55 g/d to about 130 g/d.

(II) The relationship between a peak temperature [T_(max) (°C.)] at thepeak of a dynamic mechanical loss tangent (tan δ) measured with afrequency of 110 Hz and a peak value of the dynamic loss tangent [(tanδ)_(max) ] is represented by the formula:

    (tan δ).sub.max ≧1×10.sup.-2 (T.sub.max -105)

and the (tan δ)_(max) is about 0.14 to about 0.30.

(III) The dynamic mechanical loss tangent at 220° C. is at most about0.055.

The polyethylene terephthalate which can be employed in this inventioncan be prepared by any conventional methods and may be a copolymer witha small amount of a comonomer, i.e., at most about 5% by weight so asnot to adversely affect the properties of polyethylene terephthalate.The degree of polymerization of the polyethylene terephthalate employedis not particularly limited and may be within a general range capable offorming fibers. The polyethylene terephthalate employed may also containconventional additives for polyester fibers such as a delustering agent,a stabilizer and an antistatic agent.

A most characteristic feature of the polyethylene terephthalate fiberaccording to this invention resides in the above described conditions(I) and (II).

As a result of a study on the relationship between the fine structure ofan amorphous region of a polyethylene terephthalate fiber and thedyeability, it has been found that in order for the polyethyleneterephthalate fiber to have a dyeability under normal pressure, thefiber is required to fulfill the above described condition (I) and theabove described condition (II) which represents a small transformationof the fine structure of the fiber at heating, i.e., a high thermalstability of the fine structure.

In this invention the dyeability under normal pressure means that thedye absorption at 100° C. of a polyethylene terephthalate of thisinvention is the same as or greater than that of the conventionalpolyethylene terephthalate fiber at 130° C. under a pressure higher thanatmospheric.

There are several studies reported on the relationship between thedyeability of a fiber with a disperse dye and viscoelasticity of thefiber [e.g., Kenji Kamide and Seiichi Manabe, "Fine Structure ofAmorphous Region of Fiber Revealed by Dynamic Dispersion", Sen-iGakkaishi, 34, p70 (1978)]. According to these studies it is generallyconsidered that with greater tan δ values relating to a mechanicalabsorption due to the micro-Brownian movement of a main chain of fiberor with lower temperature positions at the mechanical absorption, thedyeability of the fiber more increases. On the other hand, it has beenconsidered that with greater tan δ values the mechanical propertiesdeteriorates and the thermal resistance from the viewpoint of themechanical properties decreases. However, it is known that regarding apolyethylene terephthalate fiber at a tan δ value higher than a specificvalue, i.e., usually 0.13 or more the dyeability of the fiber reverselydecreases with increased tan δ values. Accordingly the peak value (tanδ)_(max) at a tan δ-temperature curve for a polyethylene terephthalatefiber practically employed in forming clothing is less than about 0.14.Even if polyethylene terephthalate fibers having a (tan δ)_(max) ofabout 0.14 or more may be obtained by conventional methods, the fibersare not rendered dyeable under normal pressure since the above describedcondition (II) is not fulfilled. As a result of a study on therelationship between the above described condition (II) and thedyeability it has now been found that a conventional polyethyleneterephthalate fiber having a (tan δ)_(max) of about 0.14 or moreundergoes a structural transformation in a dyeing procedure and changesto a fiber having a (tan δ)_(max) less than 0.12 and a T_(max) more than115° C. and resultedly the dyeability of the fiber under normal pressurebecome impossible.

Further if the polyethylene terephthalate fiber having the abovedescribed fine structure, i.e., satisfying the condition (II) does notpossess an initial modulus at 30° C. of about 55 g/d or less, the fiberloses the suitable inherent mechanical properties of polyester fibers,and the crease resistance and the dimensional stability as a finalarticle decrease.

The conventional polyethylene terephthalate fiber obtained at a spinningspeed less than 3000 m/min. and then not drawn possesses the finestructure of the above described condition (II) but the fine structureat heating greatly transforms, i.e., the tan δ₂₂₀ is more than 0.055 andat the same time the initial modulus at 30° C. is less than 55 g/d. Thusthis fiber is not dyeable under normal pressure. Also the polyethyleneterephthalate fiber obtained at a spinning speed less than 3000 m/min.and then drawn possesses an initial modulus at 30° C. of 55 g/d or morebut does not possess the fine structure of the above described condition(II), and the T_(max) is around 130° C. and the (tan δ)_(max) is 0.10,and it is impossible to dye this fiber under normal pressure.Accordingly, the polyethylene terephthalate fulfilling the abovedescribed conditions (I), (II) and (III) in the present invention isnovel.

It is appropriate to employ the above described T_(max) and (tanδ)_(max) as the particular values representing the fine structure of anamorphous region of fiber. The T_(max) is usually positioned at 50° C.above the glass transition temperature and the (tan δ)_(max) relates tothe amount of a molecular chain in the amorphous region whose thermalmovement is activated at a temperature of the T_(max). The T_(max) and(tan δ)_(max) of this invention are values relating to a dynamicabsorption, i.e., α_(a) absorption appearing due to the micro-Brownianmovement of a molecular chain in the amorphous region.

Regarding the polyethylene terephthalate fiber, only from the viewpointof dyeability the fiber is rendered more easily dyeable with increased(tan δ) values or with decreased T_(max) values. However, it isnecessary that the fiber satisfies at least the above describedcondition (II) in order to be dyeable under normal pressure. Especiallywhen the polyethylene terephthalate fiber not undergoing false twistinghas a T_(max) of about 105° C. or less and a (tan δ)_(max) of about 0.14or more, the dyeability of the fiber is excellent.

On the other hand, as discussed below the false twist polyethyleneterephthalate fiber undergoes heat treatment in false twisting and thestructure of the fiber is stabilized and as a result, the fiber nearlysatisfies the above described condition (III). Consequently the range ofthe T_(max) and (tan δ)_(max) fulfilled by the false twist fiber capableof being dyed under normal pressure becomes broader than that of thefiber not undergoing false twisting.

Details will be firstly given of the fiber not undergoing false twistingand secondly of the false twist fiber.

As a result of a study on the relationship between the fine structure ofa fiber and the dyeability, it has been found that with the conventionalpolyethylene terephthalate fiber having a T_(max) of 120° C. or more, ifthe (tan δ)_(max) is 0.14 or more, the thermal stability of the fiberstructure decreases and the color fastness as well as the dimensionalstability decreases. However, with the polyethylene terephthalate fiberhaving an initial modulus at 30° C. of at least about 55 g/d and aT_(max) of at most about 115° C., even if the (tan δ)_(max) is 0.14 ormore, it is not necessarily observed that the thermal stability and thedimensional stability of the fiber tend to decrease. Especially when theT_(max) is about 105° C. or lower, with polyethylene terephthalate notundergoing false twisting, in some cases the thermal stability of thefiber structure rather increases with increased (tan δ)_(max) values andthis tendency of the stabilization of the fiber structure is remarkablewhen the T_(max) is about 100° C. or lower. The thermal stability of thefiber structure relates to a dynamic mechanical loss tangent at 220° C.(tan δ₂₂₀) and increases with smaller tan δ₂₂₀ values. When the tan δ₂₂₀becomes smaller, the decrease in the initial modulus accompanying a risein temperature becomes smaller. Especially when the tan δ₂₂₀ is about0.055 or less, the decrease in the initial modulus extremely becomesmall, that is, the fiber structure become very stable to heat.

Thus, the polyethylene terephthalate fiber of this invention whichsatisfy the above described conditions (I), (II) and (III) can be dyedunder normal pressure without decrease in the thermal stability,dimensional stability and mechanical properties of the fiber and at thesame time without decrease in the color fastness of the fiber. It isgenerally observed that when the (tan δ)_(max) is 0.30 or more, thethermal stability decreases the fiber does not satisfy the abovedescribed condition (III).

As described above, the polyethylene terephthalate fiber not undergoingfalse twisting according to this invention is required to have aninitial modulus at 30° C. of at least about 55 g/d. For this reason themean birefringence index (Δn) in this invention is typically about35×10⁻³ or more. The initial modulus at 30° C. in this invention means adynamic modulus at 30° C. (E'₃₀) and its measuring method is describedbelow. In order to impart excellent mechanical properties and thermalstability to the fiber in accordance with an increase in (tan δ)_(max),it is necessary to increase the E'₃₀. When the E'₃₀ is less than about55 g/d, the thermal stability of the fiber structure and dimensionalstability of the fiber as well decrease and as a result, the fiberbecomes too soft.

As a result of a study on the relationship among the structure of thepolyethylene terephthalate fiber having the above describedcharacteristic features and not undergoing false twisting according tothis invention, the mechanical properties such as tenacity, elongation,initial modulus and dynamic modulus and the dyeability, the followinghas been found.

Degree of crystallinity (χ_(c)), apparent crystal size at the (010) face(ACS) and degree of crystal orientation at the (010) face (CO) are allrelated to mechanical properties of the polyethylene terephthalate fibernot having been subjected to false twisting according to this invention.In this invention it is preferred that the χ_(c) is about 70% to about90%, the ACS is about 50Å to about 85Å and the CO is about 85% to about97%, so that the fiber of this invention has suitable properties for usein forming clothing such as a tenacity of at least about 3 g/d, anelongation of about 20% to about 60% and an initial modulus of about 55g/d to about 130 g/d. The χ_(c), ACS and CO of the present invention aremeasured by X-ray diffraction discussed below.

Further, when a mean refractive index [n.sub.∥(0) ] at the center of afiber by polarized light having an electric field vector in thedirection of the axis of the fiber is at least about 1.65, thepolyethylene terephthalate fiber not undergoing false twisting has asuitable elongation of about 20% to about 60% and dyeability, and isdesirable for use in forming clothing.

In order that the polyethylene terephthalate fiber not undergoing falsetwisting according to this invention has an initial modulus at 30° C. ofat least 55 g/d, the mean birefringence index (Δn) in the presentinvention is preferably at least about 35×10⁻³. The mean birefringenceindex (Δn) is preferably at least about 80×10⁻³ from the viewpoint ofthermal stability of the structure and is preferably at most 150×10⁻³from the viewpoint of dyeability and color fastness. When the Δn isabout 150×10⁻³ or less, the rate of decrease of dynamic modulus (E') atbetween 150° C. and 220° C., represented as E'₂₂₀ /E'₁₅₀ :E'₂₂₀, (E') at220° C.; E'₁₅₀, (E') at 150° C., becomes 0.7 or more, i.e., thestructure of the fiber is stabilized against heat and color fastnessincreases.

Furthermore, when the mean refractive index [Δ.sub.∥(0.8-0) ] betweenthe mean refractive index at the center of the cross section of a fiber[n.sub.∥(0) ] and the refractive index at a position 0.8 times from thecenter of the cross section of a fiber [n.sub.∥(0.8) ] or [n.sub.∥(-0.8)] is within the range as set forth below, and the local mean refractiveindex is distributed symmetrical around the center of the cross sectionof the fiber, the fiber has sufficient tenacity, and is improved inuneven dyeing and uneven strength and elongation.

A local mean refractive index distributed symmetrical around the centerof the cross section of a fiber means that a minimum value of the meanrefractive index (n.sub.∥) is at least about [n.sub.∥(0) -(1×10⁻³)] andthat the difference between the n.sub.∥(-0.8) and the n.sub.∥(0.8) is atmost about 50×10⁻³, preferably at most about 10×10⁻³. Values ofn.sub.∥(0), n.sub.∥(0.8), n.sub.∥(-0.8), n.sub.∥(0.8-0) and Δn aremeasured by methods using an interference microscope discussed below.

The polyethylene terephthalate fiber not undergoing false twistingaccording to this invention can be produced by heat-treating apolyethylene terephthalate fiber spun at a spinning speed of at leastabout 4000 m/min. by dry or wet heat under the specified conditions asdiscussed below. The fiber thus obtained completely satisfies bothconditions (II) and (III) as described above. For example, thestructural modification of the fiber before and after the heat treatmentin boiling water at 100° C. for 60 minutes is very small and is withinabout ±5° C. if represented by a change in the T_(max) and within about±0.02 if represented by a change in the (tan δ)_(max).

On the other hand, when the polyethylene terephthalate fiber obtained ata spinning speed of at least about 4000 m/min. is not heat-treated bydry or wet heat under the specified conditions as discussed below, thestructural modification of the fiber after the heat treatment in boilingwater at 100° C. for 60 minutes in great and the T_(max) increases byabout 10° C. or more and the (tan δ)_(max) decreases by about 0.05 ormore. Accordingly this fiber has bad thermal stability.

The polyethylene terephthalate fiber having the fine structure asdescribed above and capable of being dyed by a disperse dye under normalpressure can be produced by extruding a melt of a polymer consistingessentially of polyethylene terephthalate at a spinning speed of atleast about 4000 m/min. to form a fiber and subjecting the fiber to heattreatment at a temperature at which a dynamic modulus (E') of the fiberdeviates from a tangent line at 180° C. of a logarithm of the E' of thefiber-temperature curve (T_(min)) plus 10° C. to a temperature ofcompletion of melting (T_(m3)) at a melting curve of the fiber measuredby a differential scanning calorimeter (DSC) plus 10° C.

A first characteristic feature of this invention resides in the spinningat a spinning speed of at least about 4000 m/min. and up to about 11000m/min., preferably about 6000 m/min. to about 9000 m/min., morepreferably about 8000 m/min. to about 9000 m/min.

The spinning speed of this invention is defined as a linear velocity ofa take up roller 7 as shown in FIG. 1. When the spinning speed is lessthan about 4000 m/min., growth of the crystalline region is insufficientand accordingly the fine structure of the fiber is thermally unstableand dimensional stability at heating is inferior. The dimensionalstability at heating and the mechanical properties at high temperaturescan be quantitatively evaluated by a dynamic modulus at 220° C. (E'₂₂₀).The E'₂₂₀ is about 1 g/d or less at a spinning speed of 3000 m/min. andfurther decreases at a spinning speed of less than 3000 m/min. to causemelting among single filaments in the heat treatment after spinning.

On the other hand, at a spinning speed of about 4000 m/min. or higher,all the degree of crystallinity, the crystal perfection index and thecrystal size of the fiber rapidly increase with increased spinningspeeds. As is shown in FIG. 6, the E'₂₂₀ rapidly increases withincreased spinning speeds. In FIG. 6, a broken line shows the E'₂₂₀ of aonce wound fiber after heat treatment at 245° C. for 2 seconds at 1%extension and a solid line shows the E'₂₂₀ of a once wound fiber beforethe above described heat treatment. The E'₂₂₀ of a fiber after the heattreatment rapidly increases with increased spinning speeds up to aspinning speed of about 6000 m/min. and at a spinning speed more than6000 m/min. an increasing ratio of the E'₂₂₀ decreases and at a spinningspeed of about 9000 m/min. the E'₂₂₀ after the heat treatment becomesgreater than that before the heat treatment. Thus, from the viewpoint ofthe mechanical properties at high temperatures the spinning speed ispreferably at least about 6000 m/min., and more preferably at leastabout 8000 m/min. FIG. 7 illustrates dependency of a degree ofcrystallinity of the fiber obtained under the same conditions as in FIG.6 on a spinning speed, FIG. 8 illustrates dependency of an apparentcrystalline size at a face of (010) of the fiber obtained under the sameconditions as in FIG. 6 on a spinning speed and FIG. 9 illustratesdependency of a degree of crystal orientation at a face of (010) of thefiber obtained under the same conditions as in FIG. 6. In FIGS. 8 and 9the region of a dotted line following the left end of the solid linerepresents impossibility of evaluation.

Thus, as is clear from FIGS. 6 to 9 the degree of crystallinity, theapparent crystal size and the degree of crystal orientation of the fiberincrease by the heat treatment at 240° C., and the increase in thedegree of crystal orientation of the fibers obtained at a spinning speedof 4000 m/min. and 5000 m/min. by the heat treatment is especiallyremarkable.

A second characteristic feature of this invention is that thepolyethylene terephthalate fiber obtained at a spinning speed of atleast about 4000 m/min. is subjected to heat treatment at a temperatureranging from a temperature at which a dynamic modulus (E') of a fiberdecreases from a tangent line at 180° C. of a logarithm of the E' of thefiber-temperature curve (T_(min)) plus 10° C., i.e., (T_(min) +10)° C.to a temperature of completion of melting (T_(m3)) at a melting curve ofthe fiber measured by a differential scanning calorimeter plus 10° C.,i.e., (T_(m3) +10)° C. The temperature at which the E' decreases from atangent line at 180° C. of a logarithm of the E'-temperature curve(T_(min)) is diagrammatically shown in FIG. 10. In other words, theT_(min) is a temperature at which the difference between the E' of thetangent line and that of the logarithm of the E'-temperature curvebecomes 0.9, i.e., the difference in log E' (ΔlogE') becomes 0.04. Theheat treatment at a temperature lower than (T_(min) +10)° C. cannotrender the fiber easily dyeable and dyes the fiber in light shadeinstead. Also the heat treatment at a temperature higher than (T_(m3)+10)° C. causes melting among the single filaments, remarkably reducesthe E'₂₂₀ and deteriorates the mechanical properties at hightemperatures. Further, even if the temperature is adjusted at atemperature lower than (T_(m3) +10)° C. in a device or apparatus forheat treatment, melting or uneven dyeing of the fiber is brought aboutwhen there is a distribution of temperature in the device or apparatus.Thus it is preferred that the temperature of the device or apparatus forheat treatment employed in this invention is controlled within apredetermined temperature ±0.5° C. and that the gradient of temperaturein the device or apparatus for heat treatment is also constant.

It is preferred that the speed of a fiber passing through the device orapparatus for heat treatment is constant. In an extreme case whererunning of the fiber is stopped, melting of the fibers occurs.

Even when fibers produced by the conventional spinning and stretchingsteps are subjected to heat treatment at a temperature ranging from(T_(min) +10)° C. to (T_(m3) +10)° C., the fibers cannot be rendereddyeable under normal pressure and if the heat treatment is conductedwithout any tension, in addition to about 25% of shrinkage broughtabout, the E'₂₂₀ extremely decreases and also the mechanical propertiesdecreases. In contrast, when unstretched fibers obtained at a spinningof at least about 4000 m/min. are subjected to heat treatment in theabove described temperature range, the fibers can be rendered easilydyeable and at the same time the elongation of the fibers tends todecrease without reduction in the tenacity, and accordingly the fiberschange into those having a suitable elongation, i.e., about 10% to about60% for use in forming clothing. Furthermore, when the unstretchedfibers are subjected to heat treatment at a most suitable temperatureand a most suitable extension ratio, the fibers can be rendered dyeableunder normal pressure and, in addition, the shrinkage in boiling waterbecomes about 5% or less. On the other hand, when fibers obtained at aspinning speed less than about 4000 m/min. and without going through astretching step are subjected to the heat treatment, the initial modulusbecomes less than about 55 g/d and as a result, the excellent mechanicalproperties inherently possessed by polyethylene terephthalate remarkablydeteriorate.

In order to improve uneven dyeing of a fiber, it is necessary that thetemperature of heat treatment is strictly controlled, and it ispreferred that the temperature of heat treatment is controlled within apredetermined temperature ±0.5° C.

With increased spinning speeds the T_(min) and T_(m3) increase and thetemperature of heat treatment shifts to a higher region. The T_(min) andthe T_(m3) approximate to the following equations, respectively.

    T.sub.min =4.8×10.sup.-3 (V-4000)+205

    T.sub.m3 =3.6×10.sup.-3 (V-4000)+283

wherein V (m/min.) is a spinning speed.

The heat treatment of a fiber at a temperature ranging from (T_(min)+10)° C. to (T_(m3) +10)° C. obtained at a spinning speed of about 6000m/min. or more can remarkably render the fiber easily dyeable, andespecially the heat treatment of a fiber at a temperature ranging from(T_(min) +10)° C. to (T_(m3) +10)° C. at an extension ratio higher thanabout -20% and lower than about +5% can more remarkably render the fibereasily dyeable. The minus (-) sign of the extension ratio means that thefiber is under relaxation and shrinkage and the plus (+) sign of theextension ratio means that the fiber is under tension and elongation.

The dyeability of polyethylene terephthalate fiber obtained at aspinning speed of at least about 4000 m/min. by heat treatment can bemore improved when a higher temperature within the range of (T_(min)+10)° C. to (T_(m3) +10)° C. is employed at the heat treatment and whenthe period of time for heat treatment becomes longer. When the fiberdoes not contact the surface of a heater for heat treatment during theheat treatment, it is sufficient that the period of time for heattreatment is at most about 10 seconds. On the other hand, when the fibercontacts the surface of the heater for heat treatment during the heattreatment, any problem cannot be created if there is no difference inrelative speed between the fiber and the surface of the heater forexample using heating rollers. It is better to avoid employing a methodof the heat treatment comprises transferring the fiber in contact withthe surface of, for example, a fixed flat plate under heating wherethere is a difference in relative speed between the fiber and thesurface of the heater since fuzz is brought about in the fiber andmelting of single filaments and uneven dyeing often occur. In order toshorten the period of time for heat treatment within about one secondwhen the fiber does not contact the surface of the heater, thetemperature is preferably about 235° C. or higher.

The device or apparatus for heat treatment which can be employed in thisinvention may be any device or apparatus capable of heating at atemperature ranging from (T_(min) +10)° C. to (T_(m3) +10)° C. and itsshape is not particularly limited. For example, the polyethyleneterephthalate fiber obtained at a spinning speed of at least about 4000m/min. may be passed through a dryer with hot air whose temperature iscontrolled within the above described temperature range. Or thepolyethylene terephthalate fiber is heat-treated by winding on acylindrical, rotatable heating roller.

In FIG. 1, a melt of polyethylene terephthalate is extruded from anozzle (not illustrated) mounted in a spinhead 2 heated at apredetermined temperature, and is cooled in the atmosphere to formfilaments 1. In this apparatus a heating zone 3, for example, a heatingcylinder surrounding the extruded filaments 1 is provided on the surfaceof the nozzle, and an aspirator 4 is provided below the heating zone 3to suck and cool the filaments 1. The filaments passed through theheating zone 3 and the aspirator 4 are treated by a device 5 forproviding an oiling agent with the filaments and a device 6 for bundlingthe filaments, and then are taken up by a take up roller 7. Thefilaments thus taken up by the take up roller 7 are once wound on thetake up roller 7, and then taken out therefrom, passed through a heaterfor heat treatment 9 whose temperature is appropriately controlledwithin the above described temperature range while the filaments areelongated or loosened at a suitable extension ratio by a pair of feedrollers 8 and a pair of delivery rollers 10 and wound on a winder 11.Also the filaments 1 are wound on the take up roller 7 one to severaltimes and after the spinning speed is adjusted to about 4000 m/min. ormore, by the action of the pair of feed rollers 8 or the pair ofdelivery rollers 10 the filaments 1 is continuously subjected to heattreatment by the heater for heat treatment 9 and subsequently are woundon a winder 11.

FIG. 2 is a diagram illustrating another embodiment of an apparatususing a pair of heating rollers by which the spinning step and thesubsequently heat treatment step are continuously conducted. In FIG. 2,the number elements 1 to 6 are the same as in FIG. 1 and a melt ofpolyethylene terephthalate is extruded from a nozzle (not illustrated)mounted in a spinhead 2 heated at a predetermined temperature, and iscooled in the atmosphere to form filaments 1. In this apparatus aheating zone 3, for example, a heating cylinder surrounding the extrudedfilaments 1 is provided on the surface of the nozzle, and an aspirator 4is provided below the heating zone 3 to suck and cool the filaments 1.The filaments passed through the heating zone 3 and the aspirator aretreated by a device 5 for providing an oiling agent with the filamentsand a device 6 for bundling the filaments and then are taken up by apair of take up rollers 7, wound on the pair of take up rollers 7 one toseveral times and subsequently wound on a pair of heating rollers 12 forheat treatment one to several times. The surface temperature of the pairof heating rollers 12 is appropriately controlled within the abovedescribed temperature range. Then the filaments thus heat-treated arewound on a winder 13. The extension ratio of the filaments at the heattreatment is controlled between the pair of take-up rollers 7 and thepair of heating rollers 12 or between the pair of heating rollers 12 andthe winder 13. Further, in order to increase the effect of the heattreatment, the pair of take-up rollers 7 can be replaced by a pair ofheating rollers whose surface temperature is adjusted at the sametemperature as that of the heating rollers 12.

Thus according to this invention the desired objects of this inventioncan be achieved by a method comprising extruding a melt of a polymerconsisting essentially of polyethylene terephthalate at a spinning speedof about 4000 m/min. or more to form a polyethylene terephthalate fiber,once winding the fiber and subsequently heat-treating the fiber or amethod comprising conducting the above described spinning step and theheat treatment step continuously.

Further the fibers which can be subjected to the heat treatment mayinclude tows obtained by bundling a plurality of the polyethyleneterephthalate fiber obtained at a spinning speed of about 4000 m/min. ormore, staple fibers obtained by cutting such tows at an appropriatelength which are made run on a suitable conveyor such as a belt conveyorthrough a device or apparatus for heat treatment and such staple fibersin the form of a web or a sliver after opening or in the form of a spunyarn after spinning.

When the heat treatment of this invention is conducted in a wet heatatmosphere, a preferred temperature for heat treatment is (T_(min) +10)°C. to about 240° C. The heat treatment in a wet heat atmosphereaccording to this invention means a heat treatment by superheated steam.

When the heat treatment in a wet heat atmosphere according to thisinvention is conducted at a temperature lower than (T_(min) +10)° C.,the polyethylene terephthalate fiber spun at a spinning speed of atleast 4000 m/min. cannot be rendered easily dyeable under normalpressure but tends to be dyed in light shade. Also, when the heat treatin a wet heat atmosphere is conducted at a temperature higher than about240° C., melting of the fibers occurs sometimes and the E'₂₂₀ remarkablydecreases and as a result, the mechanical properties at high temperatureoften deteriorates. Even when the polyethylene terephthalate fiberproduced by conventional spinning and drawing steps are subjected to theheat treatment in a wet heat atmosphere at a temperature ranging from(T_(min) +10)° C. to about 240° C., the fiber cannot be rendered easilydyeable under normal pressure. In contrast, when the undrawnpolyethylene terephthalate fiber obtained at a spinning speed of atleast about 4000 m/min. are subjected to the heat treatment in a wetatmosphere at a temperature within the above describe range, the fibercan be rendered easily dyeable under normal pressure and at the sametime the elongation of the fiber tends to decrease without reduction inthe tenacity, and accordingly the fiber changes into the one having asuitable elongation, i.e., about 10% to about 60% for use in formingclothing and a shrinkage in boiling water of about 5% or less.

For superheated steam which can be employed in this invention includes amixture of air and steam, and the superheated steam can be representedby the mol ratio of air to steam (1-x)/x wherein x is a mol fraction ofsteam and at least about 0.3.

The temperature for the wet heat treatment which can be employed isabout (T_(min) +60-85x)° C. to about (290-50x)° C. With increasedspinning speeds a more preferred temperature for the wet heat treatmentshifts to a higher region within the above described range. For example,in the wet heat treatment of a fiber obtained at a spinning speed ofabout 6000 m/min. to about 8000 m/min. the temperature employed ispreferably about 225° C. to about 240° C.

In order to improve uneven dyeing of the fiber it is necessary that thetemperature for the wet heat treatment is strictly controlled, and it ispreferred that the temperature is controlled within a predeterminedtemperature ±0.5° C.

The dyeability of a polyethylene terephthalate fiber obtained at aspinning speed of at least 4000 m/min. by the wet heat treatment can bemore improved when a higher temperature within the range of (T_(min)+10)° C. to about 240° C. is employed at the wet heat treatment and whenthe period of time for the wet heat treatment becomes longer.Accordingly, with higher temperatures for the wet heat treatment theperiod of time for the wet heat treatment becomes shorter. For example,the T_(min) of a polyethylene terephthalate fiber obtained at a spinningspeed of about 4500 m/min. is generally about 212° C. to about 213° C.,and in order to render the fiber dyeable under normal pressure by theheat treatment in superheated steam at a temperature of (T_(min) +10)°C., i.e., about 222° C. to about 223° C., the period of time for the wetheat treatment is preferably about 0.1 to about 10 seconds, and by theheat treatment in superheated steam at a temperature of about 230° C.periods of time for the wet heat treatment of about 0.01 to about 0.8second can provide the dyeability of the same degree and it is possibleto employ a period of time for the wet heat treatment longer than about0.8 second.

The device or apparatus for the wet heat treatment which can be employedin this invention may be any device or apparatus capable of providing awet heat atmosphere at a temperature of (T_(min) +10)° C. to about 240°C. and its shape is not particularly limited. For example, thepolyethylene terephthalate fiber obtained at a spinning speed of atleast about 4000 m/min. may be passed through a cylinder into whichsuperheated steam having a temperature within the above described rangeis jetted or through a cylinder whose external periphery is heated by anelectric heater and into which superheated steam having a temperaturewithin the above described range is jetted. On the polyethyleneterephthalate fiber may be placed in an autoclave into which superheatedsteam or saturated steam is blown.

In the wet heat treatment according to this invention, when apolyethylene terephthalate fiber obtained at a spinning speed of atleast 4000 m/min. is subjected to the wet heat treatment at an extensionratio of at least about -20% and less than about +5%, the mechanicalproperties of the fiber are superior to those of the fiber obtainedwithout being set in the longitudinal direction of the fiber i.e., bykeeping both ends of the fiber free during the wet heat treatment. Whenthe fiber is subjected to the wet heat treatment keeping both ends ofthe fiber free, the tenacity of the fiber is almost the same as thatbefore the wet heat treatment. On the other hand, when the fiber issubjected to the wet heat treatment at an extension ratio of at leastabout -20% and less than about +5%, the tenacity of the fiber becomesgreater than that before the heat treatment. However, when the wet heattreatment is conducted at an extension ratio more than about +5%, theimprovement on dyeability is small and as a result, the fiber cannot berendered dyeable under normal pressure.

When the polyethylene terephthalate fiber obtained at a spinning speedof at least about 4000 m/min. is subjected to the wet heat treatment ata temperature of (T_(min) +10)° C. to about 240° C. keeping both ends ofthe fiber free, the shrinkage becomes about 25% or more. In other words,even at an extensibility of about -20% the fiber heat-treated is understrain and substantially in an elongated state. It is preferred that theextension ratio at the wet heat treatment is about -5% to about 0%. Withgreater mol fractions of steam x in superheated steam for the wet heattreatment, not only the treating temperature can be lowered but alsouniformity in dyeing the treated fiber can be improved.

FIG. 3 is a diagram illustrating a further embodiment of an apparatusemployed in the process of the present invention, in which a melt ofpolyethylene terephthalate is extruded from a nozzle (not illustrated)mounted in a spinhead 2 heated at a predetermined temperature, and iscooled in the atmosphere to form filaments 1. In this apparatus aheating zone 3, for example, a heating cylinder surrounding the extrudedfilaments 1 is provided on the surface of the nozzle, and an aspirator 4is provided below the heating zone 3 to suck and cool the filaments 1.The filaments passed through the heating zone 3 and the aspirator 4 aretreated by a device 5 for providing an oiling agent with the filamentsand a device 6 for bundling the filaments, and then are wound on a pairof take-up rollers 7 one to several times to take up the filaments. Therotation of the pair of take-up rollers 7 is controlled in such a mannerthat the speed of the filaments 1 is at least about 4000 m/min. Then thefilaments are subjected to the heat treatment by superheated steam bypassing through a heating cylinder 14 for heat treatment having aplurality of slits 15 from which superheated steam is jetted into theinside of the heating cylinder, and subsequently are wound on a pair ofdelivery rollers 21 one to several times while the tension of the fiberis controlled in order not to contact the fiber with the internal wallof the heating cylinder 14, and finally wound on a winder 22. On theother hand, saturated steam having a pressure of about 10 kg/cm²produced in a boiler 20 is introduced into a device 17 for heating steamthrough a valve 19 and is heated by a heater 18 to form superheatedsteam having a temperature of (T_(min) +10)° C. to about 240° C. Thissuperheated steam is fed into a heating cylinder 14 for wet heattreatment while controlling the amount of superheated steam fed by avalve 16 and jetted through the plurality of slits 15 provided with theinternal wall of the heating cylinder 14. Thus the wet heat treatment iscontinuously carried out following the spinning step. Also after thefilaments 1 are wound on the winder 22 without being passed through theheating cylinder 14 for wet heat treatment, the filaments are subjectedto wet heat treatment by a separatedly provided device or apparatus forwet heat treatment.

FIG. 4 is a diagram illustrating one embodiment of an apparatus for thewet heat treatment of a bundle of the polyethylene terephthalate fibersobtained at a spinning speed of at least about 4000 m/min. and nothaving undergone any subsequent wet heat treatment, such as a tow and asliver, in which a fiber bundle 23 is drawn up by a pair of feed rollers24 and reaches a guide roller 25 which guides the fiber bundle into adevice 27 for wet heat treatment. At the inlet and the outlet of thedevice 27 for wet heat treatment are provided slits 26 and 26',respectively which prevents the change in the internal temperature ofthe device 27 for wet heat treatment by the external atmosphere. In thedevice 27 for wet heat treatment a number of slits 28 are provided onthe internal wall of a passage of the fiber bundle 23 and superheatedsteam is jetted simultaneously at the upper and under surfaces of thefiber bundle 23 through the slits 28. Also in the device 27 for wet heattreatment heaters 29 are provided to control the temperature ofsuperheated steam. Saturated steam having a pressure of about 10 kg/cm²produced in a boiler 36 is fed into a device 33 for heating steamthrough a valve 35 and is heated by a heater 34 to form superheatedsteam having a temperature of (T_(min) +10)° C. to about 240° C. Thissuperheated steam is fed into a device 27 for wet heat treatment througha valve 32 and are jetted at the fiber bundle 23 from the slits 28 whilecontrolling the temperature distribution therein not to increase byheaters 29. The fiber bundle 23 having undergone the wet heat treatmentis passed through the slit 26' to lead to a guide roller 30 and is takenup by a take-up roller 31.

Further, when the fiber is used in the field where the modulus and thetenacity of the fiber are required to be increased and the elongation isrequired to be reduced, the fiber after the heat treatment by dry heator wet heat may be subjected to stretching. When such stretching isconducted at a stretching ratio of about 1.05 to about 2.0 at atemperature below about 110° C., the mechanical properties are improvedand the dyeability does not change.

According to this invention a melt of a polymer consisting essentiallyof polyethylene terephthalate may be extruded at a spinning speed of atleast about 4000 m/min. to form a fiber, once wound and subsequentlysubjected to the wet heat treatment or the wet heat treatment may becontinuously conducted following the spinning step. Since thetemperature of the fibers at the time of winding is preferably lower, itis preferred for practical purposes including the temperature of wetheat treatment and the amount of the fiber to be wet heat-treated thatthe wet heat treatment is discontinuously conducted after the spinningstep.

Further the fibers which can be subjected to the wet heat treatment mayinclude tows obtained by bundling a plurality of the polyethyleneterephthalate fiber obtained at a spinning speed of about 4000 m/min. ormore, staple fibers obtained by cutting such tows at an appropriatelength which are made run on a suitable conveyor such a belt conveyorthrough a device or apparatus for wet heat treatment, such tows orstaple fibers placed in cans having a number of holes which are chargedin an autoclave for wet heat treatment and such staple fibers in theform of a web or a sliver after opening or in the form of a spun yarnafter spinning.

Details will now be given of the false twist polyethylene terephthalatefiber of this invention.

As a result of a study on the relationship between the fine structure ofan amorphous region of a false twist polyethylene terephthalate fiber,and the dyeability, it has been found that in order for the false twistpolyethylene terephthalate fiber to have a dyeability under normalpressure, the fiber is also required to satisfy the above describedconditions (II) and (III) as in the polyethylene terephthalate fiber notundergoing false twisting. False twist fibers of unmodified polyethyleneterephalate which satisfy the above described conditions (II) and (III)are not known and conventional false twist polyethylene terephthalatefibers cannot be dyed under normal pressure and the T_(max) and the (tanδ)_(max) of such conventional false twist polyethylene terephthalatefibers are 130° C. or higher and 0.14 or less, respectively.

The fine structure of the false twist fiber is thermally stabilized atfalse twisting and accordingly, the behavior at dyeing of the falsetwist fiber is different from the fiber before false twisting. Forexample, when the T_(max) of a fiber capable of being dyed under normalpressure before false twisting is about 105° C. or lower and the (tanδ)_(max) is about 0.14 or more, the dyeability increases. Also when theT_(max) is about 105° C. or lower, the dyeability increases withincreased (tan δ)_(max) values without any particular limitation to the(tan δ)_(max) only from the viewpoint of dyeability. Also the falsetwist fiber can be remarkably rendered easily dyeable with greater (tanδ)_(max) values or with low T_(max) values. However, in order for thefalse twist fiber to be dyeable under normal pressure the false twistfiber is required to satisfy at least the above described condition(II). Generally when false twisting is conducted at a temperature ofabout 180° C. or higher, the false twist fiber nearly satisfies theabove described condition (III). In order for the false twist fiber tosatisfy the above described condition (II), for example, it is necessarythat the fiber before false twisting is obtained by winding at aspinning speed of about 4000 m/min. or more and subsequentlyheat-treating the fiber once wound at a high temperature, typically atabout 230° C. or higher for a short period of time, typically shorterthan about two seconds by dry heat or heat-treating the fiber once woundby wet heat such as superheated steam at a temperature of (T_(min) +10)°C. to about 240° C. On the other hand, in conducting false twisting ofan unstretched fiber obtained at a spinning speed less than about 4000m/min. or a stretched fiber obtained by subsequently stretching such anunstretched fiber, it is usual to employ a heat setting temperature ofabout 150° C. to about 215° C. and a load of about 0.15 g/d Tex to about0.5 g/d Tex in the twisting - heat setting - untwisting procedure inorder to reduce in change of the dyeability before or after falsetwisting, to improve heat setting and to reduce in disappearance ofcrimping. The false twist fiber obtained under these conditions has aT_(max) of about 135° C., a (tan δ)_(max) of about 0.10 and nearly thesame dyeability as the fiber before false twisting or a slightlyimproved dyeability compared with the fiber before false twisting, andaccordingly cannot be said to be dyeable under normal pressure. In orderto more improve the dyeability of the false twist fibers of thisinvention, the T_(max) is about 115° C. or lower and at the same timethe (tan δ)_(max) is about 0.14 or more. In this case, however, growthof a crystalline region is essential to increase the thermal stability.

The false twist polyethylene terephthalate fiber of this invention isrequired to have an initial modulus at 30° C. of at least about 55 g/din order to have the suitable inherent properties of polyester fibers.For this reason the (tan δ)_(max) is required to be at most about 0.30.

It is preferred that the false twist polyethylene terephthalate fiber ofthis invention has a number of crimp of at least about 500/m. and acrimp stretchability of at least about 100%.

As with the polyethylene terephalate fiber not undergoing falsetwisting, the χ_(c), ACS and CO are all closely related to thedeformation of the false twist polyethylene terephalate fiber by theexternal influence and the thermal stability of the structure. In thisinvention it is preferred that the χ_(c) is about 70% to about 90%, theACS is about 50Å to about 85Å and the CO is about 85% to about 97%, sothat the false twist fiber of this invention has suitable properties asthe polyester crimp fiber such a tenacity of at least about 3 g/d, anelongation of about 20% to about 60% and an initial modulus of about 55g/d to about 130 g/d. On the other hand, the conventional false twistfiber has a χ_(c) of about 20% to about 30%, an ACS of about 30Å and aCO of about 85%.

As a typical embodiment of a process for producing the false twist fiberof this invention, an undrawn polyethylene terephthalate fiber wound ata spinning speed of about 5000 m/min. is heat-treated in a tube heaterwhose surface temperature is 255° C. for 0.6 second at 0% extensionwithout contacting the surface of the heater and subsequently issubjected to false twisting at 200° C. and at an over feed ratio of 5%.

It is preferred from the viewpoint of dyeability under normal pressureof the false twist fiber that the polyethylene terephalate fiber beforefalse twisting in this invention is required to have a (tan δ)_(max) ofabout 0.14 or more, a T_(max) of about 115° C. or lower and an initialmodulus at 30° C. of at least about 55 g/d. Also it is preferred thatthe false twist polyethylene terephthalate fiber has a smaller tan δ₂₂₀due to the small decrease in the initial modulus accompanying anincrease of temperature in the vicinity of 200° C. When the tan δ₂₂₀ isabout 0.005 or less, the decrease in the initial modulus accompanying anincrease of temperature is remarkably reduced, and the structure of thefiber becomes extremely stable to heat.

In the present invention, a fiber before false twisting having desirableproperties can be prepared with good efficiency of spinning when coolingand solidification and dimensional transformation of a polyethyleneterephthalate polymer extruded from a nozzle are controlled byregulating conditions such as polymer viscosity, spinning temperature,conditions of the atmosphere below the nozzle, the method for coolingextruded filaments and the speed of spinning. It is important to controlthe cooling and solidification of extruded filaments since suddencooling and solidification of extruded filaments and cooling andsolidification by use of cooling air having a low temperature in asingle direction crossing at a right angle to the filaments, are notpreferred to achieve good efficiency of spinning and desirableproperties. Also the above described fiber before false twisting in thisinvention can be employed as the fiber for false twisting.

The fiber before false twisting is subjected to false twisting by aconventional false twisting apparatus as shown in FIG. 5. The falsetwist fiber of this invention has a good dyeability at atmosphericpressure at 100° C., and the structural transformation against heatgiven in the procedure of preparing a final product is small due to theparticular fine structure and is especially useful as the fiber informing clothing.

The polyethylene terephthalate fiber of this invention includesmonofilaments, flat yarns and false twist yarns of monofilaments andmultifilaments, tows, staple fibers or cut fibers having anappropriately cut length and crimps as the starting material forspinning, webs obtained by opening the staple fibers, slivers made fromthe webs and spun yarns made from the slivers. Since the polyethyleneterephalate fiber of this invention has the fine structure as defined inthis invention, the fiber can be dyed by a disperse dye under normalpressure and accordingly can be dyed without using a carrier by a normalpressure dyeing machine. For this reason, it is possible to dye not onlyproducts solely made of the polyethylene terephthalate fibers but alsoproducts made of the polyethylene terephthalate fibers in admixture withacrylic fibers, wool or spandex fibers without rendering the acrylicfibers, wool or spandex fibers brittle, which has been considereddifficult. Further there can be obtained dyed products made of thepolyethylene terephthalate fibers in admixture with regeneratedcellulose fibers and having excellent mechanical properties. Also inprinting, steaming under normal pressure is possible with products madeof the polyethylene terephthalate fibers or its admixture with acrylicfibers, wool, spandex fibers or regenerated cellulose fibers and thusreduction in cost is favorably brought about and there can be obtainedprinted products thereof having excellent hand touchness and mechanicalproperties.

Methods for Measuring Parameters to Be Used for Specifying theStructural Properties of the Present Invention A. Dynamic MechanicalLoss Tangent (tan δ) and the Dynamic Modulus (E')

The dynamic mechanical loss tangent (tan δ) and the dynamic modulus (E')can be measured by using an apparatus for direct reading dynamicviscoelasticity manufactured by Toyo Baldwin, Rheo-Vibron DDV-IIc, at afrequency of 110 Hz, in dry air and at a temperature increasing at arate of 10° C./min.

A peak temperature (T_(max)) of tan δ and a peak value [(tan δ)_(max) ]of tan δ are obtained from the tan δ-temperature curve. Typicalembodiments of a tan δ-temperature curve and an E'-temperature curve areillustrated in FIGS. 11(a) and 11(b), wherein (A) represents a fiber ofthe present invention, (B) represents a conventional stretched fiber,(C) represents an unstretched fiber and (D) represents a partiallyoriented fiber.

B. Apparent Crystal Size (ACS)

ACS can be determined by measuring the X-ray diffraction intensity inthe equatorial direction by the reflection method. The measurement iscarried out by using an X-ray generator (RU-200PL manufactured by RigakuDenki), a goniometer (SG-9R manufactured by Rigaku Denki), ascintillation counter and a pulse height analyzer. Cu-K.sub.α(wavelength λ=1.5418 Å) monochromatized by a nickel filter is used forthe measurement. The fiber sample is set in a sample holder composed ofaluminum so that the fiber axis is perpendicular to the plane of thediffraction. The thickness of the sample is adjusted to about 0.5 mm.

The X-ray generator is operated at 30 kV and 80 mA. The diffractionintensity is recorded from 7° to 35° of 2θ at a scanning speed of1°/min., a chart speed of 10 mm/min., a time constant of 1 second, adivergent slit of 1/2°, a receiving slit of 0.3 mm, and a scatteringslit of 1/2°. The full scale deflection of the recorder is set so thatthe entire diffraction curve remains on the scale.

Generally, a polyethylene terephthalate fiber has three majorreflections on the equatorial line in the range of from 17° to 26° of 2θ(at faces of (100), (010), and (110)). FIG. 12 is a graph of oneembodiment illustrating a curve of X-ray diffraction intensity of apolyethylene terephthalate fiber, in which (e) is a portion the X-raydiffraction intensity attributed to the crystalline region and (f) is aportion of the X-ray diffraction intensity attributed to the amorphousregion.

For example, ACS is determined according to the equation of Scherrerdescribed in L. E. Alexander, X-ray Diffraction Methods in PolymerScience, Chapter 7, published by John Wiley & Sons, Inc., New York.

A base line is established by drawing a straight line between 7° and 35°of 2θ on the diffraction intensity curve. A vertical straight line isdropped from the diffraction peak, and the mid-point between the peakand the base line is marked. A horizontal line passing through themid-point is drawn on the diffraction intensity curve. If the two majorreflections are sufficiently separated from each other, this lineintersects shoulders of the two peaks of the diffraction intensitycurve, but if they are not sufficiently separated, the line intersectsone shoulder alone. The width of the peak (half value width) ismeasured. If the line intersects one shoulder alone, the distancebetween the intersecting point and the mid-point is measured anddoubled. If the line intersects two shoulders, the distance between thetwo shoulders is measured. The measured value is converted to a linebreadth in radians and the line breadth is corrected according to theformula: ##EQU1## wherein B is the observed line breadth, and b is thebroadening constant in radians, which is determined by the half valuewidth of the reflection peak of a silicon single crystal at the face(111) thereof.

The apparent crystal size is given by the formula:

    ACS (Å)=K·λ/β cos θ

wherein K is taken as one, λ is the X-ray wavelength (1.5418 Å), β isthe corrected line breadth and θ is the Bragg angle (half of 2θ).

C. Degree of Crystallinity (χ_(c))

A base line is established by drawing a straight line between 7° and 35°of 2θ on the diffraction intensity curve, which is derived by the samemethod used to measure ACS. As shown in FIG. 12, the crystalline portionand tne amorphous portion are separated by drawing a straight line alongthe tail of the lower angle and the tail of the higher angle from thepeak point positioned near the angle of 20° of 2θ. The χ_(c) isrepresented by an area analysis method according to the followingequation: ##EQU2##

D. Degree of Crystal Orientation (CO)

The degree of crystal orientation is measured by using an X-raygenerator (for example, RU-200PL manufactured by Rigaku Denki), a fibermeasuring device (FS-3 manufactured by Rigaku Denki), a goniometer (SG-9manufactured by Rigaku Denki), a scintillation counter and a pulseheight analyzer.

Cu-Kα (wavelength λ=1.5418 Å) monochromatized by a nickel filter is usedfor the measurement. Generally, although a polyethylene terephthalatefiber has three major reflections on the equatorial line, the reflectionat the (010) face is used in the measurement of the CO. The 2θ value ofthe reflection of the (010) face used is determined from the curve ofthe diffraction intensity in the equatorial direction.

The X-ray generator is operated at 30 kv and 80 mA. The fiber sample isattached to the fiber measuring device so that filaments are parallel toone another.

Preferably the sample thickness is about 0.5 mm. The goniometer is setat the 2θ value determined by the diffraction intensity curve in theequatorial direction. Scanning is conducted in the range of from -30° to+30° in the azimuthal direction according to a method of transmission,and the diffraction intensity in the azimuthal direction is recorded bythe scintillation counter. Furthermore, the diffraction intensity at-180° in the azimuthal direction and the diffraction intensity at +180°in the azimuthal direction are recorded. At this measurement, thescanning speed is 4°/min., the chart speed is 10 mm/min., the timeconstant is 1 second, the collimeter is characterized by 2 mmφ and thereceiving slit has a length of 19 mm and a width of 3.5 mm.

The CO value is determined from the obtained diffraction intensity curvein the azimuthal direction according to the following procedures. A meanvalue of the diffraction intensity value obtained at ±180° is evaluated,and a horizontal line (a base line) is drawn to pass through the pointof the mean value. A perpendicular line is drawn to the base line fromthe peak, and the mid-point of the perpendicular line is determined anda horizontal line passing through the mid-point is drawn. The distancebetween two intersecting points of the horizontal line and thediffraction intensity curve is measured and the measured value isconverted to an orientation angle H(°) in degrees (°). The degree ofcrystal orientation (CO) is represented by the equation: ##EQU3##

E. Mean Refractive Index (n.sub.∥, N.sub.⊥) and Mean Birefringence Index(Δn)

According to the interference fringe method using a transmissionquantitative type interference microscope (for example, an interferencemicroscope "Interphako" manufactured by Carl-Zeiss Yena Co., EastGermany), the distribution of the mean refractive index, observed fromthe side face of the fiber, can be determined. This method can beapplied to fibers having a circular cross section.

The refractive index of fibers is characterized by a refractive index topolarized light having an electric field vector in the directionparallel to the fiber axis (n.sub.∥) and a refractive index to polarizedlight having an electric field vector in the direction perpendicular tothe fiber axis (n.sub.⊥).

Refractive indices (n.sub.∥ and n.sub.⊥) obtained by using greenradiation (wavelength λ=549 mμ) are employed. The fiber to be tested isimmersed in a medium inert to fibers having a refractive index (N)giving a deviation of the interference fringe in the range of 0.2 to 2.0times the wavelength by using optical flat slide glass and cover glass.

The refractive index (N) of the medium is a value measured at 20° C. byan Abbe refractometer using green radiation (wavelength λ=549 mμ).

Several filaments are immersed in the medium so that the filaments arenot in contact with one another. The fiber should be disposed so thatthe fiber axis is perpendicular to the optical axis of the interferencemicroscope and the interference fringe. The pattern of the interferencefringe is photographed and enlarged at about 1,500 magnifications foranalysis.

Referring to FIG. 13, the optical path difference Γ is represented bythe formula: ##EQU4## wherein N is the refractive index of the medium,n.sub.∥ (or n.sub.⊥) is the refractive index between S^(I) -S^(II) atthe periphery of the fiber, t is the thickness between S^(I) -S^(II), λis the wavelength of the radiation used, D is the distance(corresponding to 1λ) between parallel interference fringes of thebackground and d is the deviation of the interference fringe by thefiber.

From optical path differences at respective positions in the range ofthe center of the fiber (R_(o)) to the periphery of the fiber (R), thedistribution of the refractive index n.sub.∥ (or n.sub.⊥) of the fiberat the respective positions can be determined. When r is the distancefrom the center of the fiber to the respective position, the refractiveindex at the center of the fiber, i.e., X=r/R =0 is defined as the meanrefractive index [n.sub.∥(0) or n.sub.⊥(0) ]. X is 1 at the position ofthe periphery of the fiber, but X is a value of 0 to 1 at the otherposition of the fiber.

For example, n.sub.∥(0.8) (or n.sub.⊥(0.8)) represents the refractiveindex at the position of X=0.8. From the mean refractive indicesn.sub.∥(0) and n.sub.⊥(0), the mean birefringence index (Δn) isrepresented as Δn=n.sub.Ξ(0) -n.sub.⊥(0). In FIG. 13, 37 is the fiber;38 is the interference fringe by the medium; and 39 is the interferencefringe by the fiber. Δn.sub.(0.8-0) means a difference in Δn between X=0and X=0.8. With a fiber having a modified cross section the refractiveindex determined by the Becke line method is defined as X=0.8 andfurther the refractive index of the medium at Γ=0, i.e., d=0, observedby an interference microscope, is defined as a refractive index at X=0.

F. Shrinkage in Boiling Water

Shrinkage in boiling water is represented by the equation: ##EQU5##wherein L_(o) is the length of a sample under the load of 0.1 g/d, and Lis the length of the sample under the initial load of 0.1 g/d after thetreatment in boiling water without the load for 30 minutes.

G. Melting Completion Temperature (T_(m3))

A melting curve is measured by heating about 1.5 mg of a sample in a N₂gas atmosphere from a temperature of about 180° C. at a rate ofincreasing the temperature of 20° C./min. using a differential scanningcalorimeter (DSC-1b manufactured by Perkin-Elmer). The T_(m3) is definedas a temperature of completion of melting at the melting curve asindicated in FIG. 14. The T_(m2) is a peak temperature and the T_(m1) isa temperature of initiation of melting.

H. Dyeability

The dyeability is evaluated by a degree of dye exhaustion. A sample isdyed with a disperse dye (Resolin Blue FBL, C.I. Disperse 56, Tradenameof Bayer in Federal Republic of Germany) at a dye concentration of 3%owf and a liquor ratio of 1 to 50 at 100° C. Further a dispersing agent(Disper TL) of 1 g/l is added to the dyeing solution, and then aceticacid is added to condition the pH of the solution to 6.

After a predetermined period of time of dyeing (one hour), part of thedyeing solution is collected and the amount of dye remaining in thedyeing solution is measured by absorbance at 625 mm. Then the amount ofdye exhausted is obtained by subtracting the remaining amount of dyefrom the amount of dye employed in dyeing. The dye exhaustion ratio iscalculated by dividing this exhausted amount of dye by the amount of dyeemployed and multiplying the result by 100.

The sample which is scoured with Scourol FC-250 (tradename of Kao-Atlas)of 2 g/l at 60° C. for 20 minutes, dried, and conditioned at a relativehumidity of 65% at 20° C. for 24 hours is employed.

Whether a fiber can be dyed under normal pressure or not is determinedby comparing the dye exhaustion of the fiber with that of a conventionalpolyethylene terephthalate fiber which is dyed at 130° C. for 60 minutesunder the above described conditions, i.e., 80%. If the dye exhaustionof a fiber is 80% or more, the fiber can be judged to have a gooddyeability under normal pressure.

I. Color Fastness of Dyed Fibers

The sample is dyed by the same method as in the evaluation of dyeabilitydescribed above except that the concentration of dye is 1% owf anddyeing time is 90 minutes. Further, the sample is carried out reductioncleaning with sodium hydrosulfate of 1 g/l and sodium hydroxide of 1g/l, and a surface active agent (Sunmol RC-700) of 1 g/l at a liquorratio of 1 to 50 at 80° C. for 20 minutes.

The samples are evaluated according to JIS-L-1044 for color fastness tolight, JIS-L-0489 for color fastness to rubbing and JIS-L-0854 for colorfastness to sublimation. The judgement of these evaluations is given by5 grades, from 1 for the lowest to 5 for the highest and determined byexamination with the naked eye.

J. Initial Modulus

Initial Modulus is the value of the dynamic modulus (E') at 30° C.obtained by measuring the dynamic modulus as described above.

K. Tenacity and Elongation

Tenacity and elongation are measured using a tensile testing machine,Tensilon UTM-II-20 manufactured by Toyo Baldwin, at an initial length of5 cm and a tensile velocity of 20 mm/min. with a fiber having a crimp,the initial length of 5 cm employed is the length of the crimpelongated.

L. Crimp Retention

Of the rate of crimp appearance described in Japanese Patent application(OPI) No. 35112/1973, the CD₅.0 is employed. First, the CD₅.0 of atextured yarn obtained by the stretchingfalse twisting procedure isdesignated as α. Second, the textured yarn under a load of 0.1 g/d isimmersed in boiling water at 100° C. for one minute and subsequently isspontaneously dried at 20° C. at a relative humidity of 60% in keepingboth ends of the yarn free and left to stand at 20° C. at a relativehumidity of 60% for 24 hours. Then the CD₅.0 of the textured yarn thustreated is measured again and designated as β. The crimp retention isrepresented by the equation:

    Crimp retention (%)=β/α×100

Usually the crimp retention of 65% or more is judged to be good.

The present invention will now be illustrated in detail by the followingexamples.

EXAMPLE 1

Polyethylene terephthalate having an intrinsic viscosity [η] of 0:63 dl/g, which was measured in a mixed solvent of a 2:1 volume ratio ofphenol and tetrachloroethane at 35° C., was extruded from a nozzlehaving 7 fine holes 0.35 mm in diameter at a spinning temperature of300° C. The filaments extruded were cooled and solidified with a streamof air at 22° C. supplied from the direction of all the circumference ofthe fiber in the parallel direction of the running filaments and then,after adding an oiling agent, the filaments were wound at a spinningspeed of 3000 m/min. to 7000 m/min. to give multifilaments of 35d/7f.Subsequently the wound multi-filaments were subjected to heat treatmentby passing through a heater for heat treatment 9 as shown in FIG. 1whose internal temperature was adjusted at 240°±0.5° C. for one secondat 1.5% extension without any contact with the surface of the heater.

The features of the fine structure and mechanical properties of thepolyethylene terephthalate fiber thus obtained are shown in Table 1. Thefibers of Run Nos. 1 to 4 belong to this invention and those of Run Nos.5 to 7 are outside this invention. It can be understood that the fibersof this invention prepared in Run Nos. 1 to 4 have adequate mechanicalproperties, thermal stability, dyeability under normal pressure andcolor fastness. On the other hand, the fibers outside this inventionprepared in Run Nos. 5 to 7 are not sufficient in all these properties.

                                      TABLE 1                                     __________________________________________________________________________                                      Refractive Index                            Spinning         Dynamic Viscoelastic Properties                                                                              Distribution                       Speed       T.sub.max                                                                        (tan δ).sub.max                                                               tan δ.sub.220                                                                E'.sub.30                                                                        Δn                                                                           n.sub.//(0)                                                                      Δn.sub.//(0.8-0)                                                              of Local                      Run No.                                                                            (m/min.)                                                                           Draw Ratio*.sup.1                                                                    (°C.)                                                                     (-)   (-)  (g/d)                                                                            (× 10.sup.-3)                                                                (-)                                                                              (× l0.sup.-3)                                                                 Refractive                    __________________________________________________________________________                                                    Index                         1    7000 --     94 0.150 0.024                                                                              73 120  1.692                                                                            15    symmetry                      2    6000 --     95 0.170 0.030                                                                              70 117  1.684                                                                            9     "                             3    5000 --     96 0.200 0.045                                                                              69  91  1.666                                                                            7     "                             4    4000 --     98 0.210 0.050                                                                              67  59  1.649                                                                            5     "                             5*.sup.2                                                                           3000 --     95 0.320 0.060                                                                              35  30  1.592                                                                            4     "                             6*.sup.2                                                                           1500 3.3    135                                                                              0.105 0.035                                                                              97 173  1.691                                                                            2     "                             7*.sup.2                                                                           1000 4.0    137                                                                              0.100 0.037                                                                              102                                                                              182  1.693                                                                            2     unsymmetry                    __________________________________________________________________________                Mechanical & Thermal Properties                                                                       Degree                                    Crystal Structure                                                                                    Shrinkage in of Dye                                    Run                                                                              χc                                                                           ACS                                                                              CO Tenacity                                                                           Elongation                                                                          Boiling water                                                                              Exhaustion                                                                          Color Fastness                      No.                                                                              (%)                                                                              (Å)                                                                          (%)                                                                              (g/d)                                                                              (%)   (%)    E'.sub.220 /E'.sub.150                                                              (%)   Light                                                                             Rubbing                                                                            Sublimation                __________________________________________________________________________    1  76 55 95 4.3  38    2.9    0.75  94    4˜5                                                                         5    4                          2  70 51 92 4.1  47    2.9    0.72  93    4˜5                                                                         4˜5                                                                          3˜4                  3  52 48 87 3.6  56    3.1    0.70  93    4˜5                                                                         4˜5                                                                          3                          4  31 40 85 2.7  61    3.5    0.69  90    4˜5                                                                         5    3                          5* 26 23 51 2.1  82    32.0   0.65  80    4˜5                                                                         5    3                          6* 62 18 90 5.0  23    7.8    0.55  45    3   4˜5                                                                          3                          7* 56 20 91 5.1  21    8.2    0.56  51    3   4˜5                                                                          3                          __________________________________________________________________________     *.sup.1 Draw ratio at 160° C.                                          *.sup.2 Fibers of Run Nos. 5 to 7 are outside the scope of this invention                                                                              

EXAMPLE 2

Polyethylene terephthalate having a [η] of 0.63 dl/g was extruded from anozzle having 7 fine holes 0.35 mm in diameter at a spinning temperatureof 300° C. The filaments extruded were cooled and solidified with astream of air at 22° C. supplied from the direction of all thecircumference of the fiber in the parallel direction of the runningfilaments and then, after adding an oiling agent, the filaments werewound at a spinning speed of 4000 m/min. to 9000 m/min. to givemultifilaments of 35d/7f. Subsequently the multifilaments thus obtainedwere subjected to heat treatment by passing through a heater for heattreatment 9 as shown in FIG. 1 whose internal temperature was adjustedat 245° C. for 0.8 second at 2% extensibility without any contract withthe surface of the heater.

The features of the fine structure and mechanical properties of thepolyethylene terephthalate fiber thus obtained are shown in Table 2.

As a reference, the fiber of 35d/7f having been spun at a spinning speedof 3000 m/min. and the fiber of 35d/7f having been spun at a spinningspeed of 1500 m/min. and then drawn at 130° C. at a draw ratio of 3.3were subjected to the same heat treatment as described above. Theproperties of these fibers are also shown in Table 2.

From Table 2 it can be understood that the fibers having been obtainedat a spinning speed of 4000 m/min. or more and then heat-treated at 245°C. for 0.8 second at 2% extension are rendered easily dyeable and areexcellent in color fastness and fully satisfactory in mechanicalproperties and thermal stability. In contrast, the fiber having beenobtained at a spinning speed of 3000 m/min. and then heat-treated underthe above described conditions is rendered easily dyeable but is poor inmechanical properties, and the fiber having been obtained at a spinningspeed of 1500 m/min., drawn and then heat-treated under the abovedescribed conditions is not rendered easily dyeable.

                                      TABLE 2                                     __________________________________________________________________________                                 Refractive Index                                 Spinning    Dynamic Viscoelastic Properties                                                                        Distribution                             Run                                                                              Speed                                                                              Draw                                                                              T.sub.max                                                                        (tan δ).sub.max                                                               tan δ.sub.220                                                                E'.sub.30                                                                        Δn                                                                           n.sub.//(0)                                                                      of Local T.sub.min *.sup.3                                                                  T.sub.m.sbsb.2                                                                /T.sub.m.sbsb.3                                                               *.sup.3                    No.                                                                              (m/min.)                                                                           Ratio*.sup.1                                                                      (°C.)                                                                     (-)   (-)  (g/d)                                                                            (× 10.sup.-3)                                                                (-)                                                                              Refractive Index                                                                       (°C.)                                                                       (°C./°C.)    __________________________________________________________________________    1  9000 --  98 0.141 0.018                                                                              76 119  1.696                                                                            symmetry 230  269/297                    2  8000 --  97 0.145 0.020                                                                              77 120  1.696                                                                            "        224  268/296                    3  7000 --  93 0.152 0.023                                                                              79 121  1.695                                                                            "        219  263/294                    4  6000 --  94 0.173 0.033                                                                              80 119  1.690                                                                            "        215  254/287                    5  5000 --  96 0.204 0.047                                                                              80  96  1.681                                                                            "        213  258/282                    6  4000 --  99 0.211 0.052                                                                              57  65  1.653                                                                            "        212  256/284                    7*.sup.2                                                                         3000 --  91 0.322 0.059                                                                              38  31  1.594                                                                            "        202  257/287                    8*.sup.2                                                                         1500 3.3 134                                                                              0.106 0.037                                                                              95 176  1.692                                                                            unsymmetry                                                                             208  262/291                    __________________________________________________________________________                Mechanical & Thermal Properties                                                                       Degree                                    Crystal Structure      Shrinkage in of Dye                                    Run                                                                              χc                                                                           ACS                                                                              CO Tenacity                                                                           Elongation                                                                          Boiling water                                                                              Exhaustion                                                                          Color Fastness                      No.                                                                              (%)                                                                              (Å)                                                                          (%)                                                                              (g/d)                                                                              (%)   (%)    E'.sub.220 /E'.sub.150                                                              (%)   Light                                                                             Rubbing                                                                            Sublimation                __________________________________________________________________________    1  80 75 94 3.5  26    1.5    0.81  95    4˜5                                                                         5    4˜5                  2  78 65 94 3.8  29    1.7    0.79  95    4˜5                                                                         5    4˜5                  3  76 58 93 4.4  37    2.8    0.75  94    4˜5                                                                         5    4                          4  68 54 91 4.2  44    3.2    0.73  94    4˜5                                                                         4˜5                                                                          3˜4                  5  52 51 86 3.6  59    3.3    0.72  93    4˜5                                                                         4˜5                                                                          3                          6  32 43 83 3.5  63    4.4    0.70  91    4˜5                                                                         5    3                          7*.sup.2                                                                         28 25 49 2.3  85    31.0   0.66  81    4˜5                                                                         5    3                          8*.sup.2                                                                         60 19 88 5.1  24    7.7    0.57  43    3   4˜5                                                                          3                          __________________________________________________________________________     *.sup. 1 Draw ratio at 130° C.                                         *.sup. 2 Fibers of Run Nos. 7 and 8 are outside the scope of                  *.sup.3 T.sub.min and T.sub.m3 are values before the heat treatment.     

EXAMPLE 3

Polyethylene terephthalate having a [η] of 0.64 was extruded from anozzle having 7 fine holes 0.35 mm in diameter at a spinning temperatureof 300° C. The filaments extruded were cooled and solidified with astream of air at 22° C. supplied from the direction of all thecircumference of the fiber in the parallel direction of the runningfilaments and then, after adding an oiling agent, the filaments werewound at a winding speed of 4000 m/min. to 9000 m/min. to givemultifilaments of 35d/7f. Subsequently the multifilaments thus obtainedwere subjected to heat treatment by passing through a heater for heattreatment 9 as shown in FIG. 1 whose internal surface temperature wasadjusted at 240° C. for 0.7 second at a speed of 60 m/min. at 2%extensibility without any contact with the surface of the heater.

The features of the fine structure and properties of the polyethyleneterephthalate fiber thus obtained are shown in Table 3.

As a reference, the fiber of 35d/7f having been obtained at a spinningspeed of 3000 m/min. and the fiber of 35d/7f having been spun at awinding speed of 1500 m/min. and then drawn at 130° C. at a draw ratioof 3.3 were subjected to the same heat treatment as described above. Theproperties of these fibers are also shown in Table 3.

From Table 3 it can be understood that the fibers having been obtainedat a spinning speed of 4000 m/min. or more and then heat-treated at 240°C. for 0.7 second at 2% extension are rendered easily dyeable and areexcellent in color fastness and fully satisfactory in mechanicalproperties and thermal stability. In contrast, the fiber having beenobtained at a spinning speed of 3000 m/min. and then heat-treated underthe above described conditions is rendered easily dyeable but is poor inmechanical properties, and the fiber having been obtained at a spinningspeed of 1500 m/min., drawn at a draw ratio of 3.3 and then heat-treatedunder the above described conditions is not rendered easily dyeable.

                                      TABLE 3                                     __________________________________________________________________________                                 Refractive Index                                 Spinning    Dynamic Viscoelastic Properties                                                                        Distribution                             Run                                                                              Speed                                                                              Draw                                                                              T.sub.max                                                                        (tan δ).sub.max                                                               tan δ.sub.220                                                                E'.sub.30                                                                        Δn                                                                           n.sub.//(0)                                                                      of Local T.sub.min *.sup.3                                                                  T.sub.m2 /T.sub.m3                                                            *.sup.3                    No.                                                                              (m/min.)                                                                           Ratio*.sup.1                                                                      (°C.)                                                                     (-)   (-)  (g/d)                                                                            (× 10.sup.-3)                                                                (-)                                                                              Refractive Index                                                                       (°C.)                                                                       (°C./°C.)    __________________________________________________________________________    1  9000 --  97 0.141 0.018                                                                              76 117  1.693                                                                            symmetry 227  269/298                    2  8000 --  96 0.144 0.020                                                                              77 118  1.692                                                                            "        225  268/297                    3  7000 --  94 0.149 0.022                                                                              79 115  1.690                                                                            "        220  262/293                    4  6000 --  95 0.169 0.032                                                                              80 114  1.681                                                                            "        216  259/288                    5  5000 --  97 0.198 0.044                                                                              80  89  1.670                                                                            "        214  254/283                    6  4000 --  98 0.213 0.054                                                                              57  56  1.640                                                                            "        213  255/285                    7*.sup.2                                                                         3000 --  90 0.319 0.063                                                                              39  53  1.591                                                                            "        200  259/287                    8*.sup.2                                                                         1500 3.3 136                                                                              0.104 0.038                                                                              96 180  1.690                                                                            unsymmetry                                                                             210  263/292                    __________________________________________________________________________    Crystal    Mechanical & Thermal Properties                                                                        Degree                                    Structure             Shrinkage in  of Dye                                    Run                                                                              χc                                                                          ACS                                                                              CO Tenacity                                                                           Elongation                                                                          Boiling Water Exhaustion                                                                          Color Fastness                      No.                                                                              (%)                                                                             (Å)                                                                          (%)                                                                              (g/d)                                                                              (%)   (%)     E'.sub.220 /E'.sub.150                                                              (%)   Light                                                                             Rubbing                                                                            Sublimation                __________________________________________________________________________    1  80                                                                              77 96 3.6  25    1.3     0.82  96    4˜5                                                                         5    4˜5                  2  77                                                                              66 96 3.8  31    1.4     0.80  95    4˜5                                                                         5    4˜5                  3  75                                                                              59 95 4.4  37    2.7     0.76  94    4˜5                                                                         5    4                          4  71                                                                              52 92 4.0  45    3.0     0.74  94    4˜5                                                                         5    4                          5  52                                                                              50 88 3.6  58    3.2     0.71  93    4˜5                                                                         4˜5                                                                          3˜4                  6  34                                                                              42 86 3.4  64    4.1     0.69  92    4˜5                                                                         5    3                          7*.sup.2                                                                         27                                                                              26 50 2.1  82    32.8    0.67  84    4˜5                                                                         5    3                          8*.sup.2                                                                         63                                                                              18 91 5.2  126   7.6     0.54  46    3   4˜5                                                                          3                          __________________________________________________________________________     *.sup.1 Stretching ratio at 130° C.                                    *.sup.2 Fibers of Runs Nos. 7 and 8 are outside the scope of this             invention.                                                                    *.sup.3 T.sub.min and T.sub.m2 /T.sub.m3 are values before the heat           treatment.                                                               

EXAMPLE 4

The multifilaments of 35d/7f having a T_(min) of 212° C. andT_(m).spsb.3 of 283° C. prepared by the same procedures as in Example 3at a spinning speed of 5000 m/min. were subjected to heat treatment bypassing through a heater for heat treatment 9 as shown in FIG. 1 whoseinternal surface temperature was adjusted at a temperature shown inTable 4 for 0.8 second at 1% extension without any contact with thesurface of the heater. The dynamic viscoelastic properties, mechanicaland thermal properties and degree of dye exhaustion of the fiber thusobtained are shown in Table 4. The Δn and n.sub.∥ (0) of the fibers ofthis invention were 85×10⁻³ to 95×10⁻³ and 1.665 to 1.676, respectivelyand the distribution of local refractive index was symmetrical.

From Table 4 it can be understood that the fibers heat-treated accordingto this invention are rendered easily dyeable and have fullysatisfactory mechanical and thermal properties.

                                      TABLE 4                                     __________________________________________________________________________    Heat                       Mechanical & Thermal Properties                                                                        Degree                    Treatment Dynamic Viscoelastic Properties                                                                           Shrinkage in  of Dye                    Run                                                                              Temperature                                                                          T.sub.max                                                                        (tan δ).sub.max                                                               tan δ.sub.220                                                                E'.sub.30                                                                        Tenacity                                                                           Elongation                                                                          Boiling Water Exhaustion                No.                                                                              (°C.)                                                                         (°C.)                                                                     (-)   (-)  (g/d)                                                                            (g/d)                                                                              (%)   (%)     E'.sub.220 /E'.sub.150                                                              (%)                       __________________________________________________________________________    1*.sup.1                                                                         200    130                                                                              0.150 0.043                                                                              65 3.6  78    9.1     0.65  45                        2  225    99 0.170 0.042                                                                              76 3.6  60    3.2     0.69  93                        3  250    93 0.215 0.042                                                                              72 3.6  52    2.1     0.75  95                        4  275    91 0.250 0.050                                                                              70 3.5  45    1.3     0.68  93                        5  --*.sup.2                                                                            134                                                                              0.195 0.047                                                                              60 3.6  83    13.1    0.65  56                        __________________________________________________________________________     *.sup.1 Fiber of Run No. 1 is outside the scope of this invention.            *.sup.2 Fiber without heat treatment.                                    

EXAMPLE 5

The multifilaments of 35d/7f having a T_(min) of 230° C. and aT_(m).spsb.3 of 298° C. prepared by the same procedures as in Example 3at a spinning speed of 9000 m/min. were subjected to heat treatment bypassing through a heater for heat treatment 9 as shown in FIG. 1 whoseinternal surface temperature was adjusted at a temperature shown inTable 5 for 1 second at 1% extension without any contact with thesurface of the heater. The dynamic viscoelastic properties, mechanicaland thermal properties and degree of dye exhaustion of the fibers thusobtained are shown in Table 5. The Δn and n.sub.∥ (0) of the fibers ofthis invention were 109×10⁻³ to 116×10⁻³ and 1.694 to 1.701,respectively and the distribution of local refractive index wassymmetrical.

According to this invention, polyethylene terephthalate fibers can berendered easily dyeable without accompanying deterioration of mechanicaland thermal properties.

                                      TABLE 5                                     __________________________________________________________________________    Heat                       Mechanical & Thermal Properties                                                                        Degree                    Treatment Dynamic Viscoelastic Properties                                                                           Shrinkage in  of Dye                    Run                                                                              Temperature                                                                          T.sub.max                                                                        (tan δ).sub.max                                                               tan δ.sub.220                                                                E'.sub.30                                                                        Tenacity                                                                           Elongation                                                                          Boiling Water Exhaustion                No.                                                                              (°C.)                                                                         (°C.)                                                                     (-)   (-)  (g/d)                                                                            (g/d)                                                                              (%)   (%)     E'.sub.220 /E'.sub.150                                                              (%)                       __________________________________________________________________________    1*.sup.1                                                                         200    102                                                                              0.125 0.018                                                                              76 3.5  25    2.5     0.80  63                        2*.sup.1                                                                         220    101                                                                              0.124 0.018                                                                              76 3.5  25    2.3     0.80  69                        3  250    94 0.145 0.016                                                                              78 3.6  23    1.4     0.83  87                        4  270    90 0.210 0.043                                                                              75 3.5  28    1.4     0.81  93                        5  280    89 0.215 0.050                                                                              74 3.4  27    1.3     0.80  94                        6  --*.sup.2                                                                            102                                                                              0.126 0.018                                                                              74 3.5  25    2.9     0.79  60                        __________________________________________________________________________     *.sup.1 Fibers of Run Nos. 1 and 2 are outside the scope of this              invention.                                                                    *.sup.2 Fiber without heat treatment.                                    

EXAMPLE 6

The multifilaments of 35d/7f having a T_(min) of 212° C. and aT_(m).spsb.3 of 285° C. prepared by the same procedures as in Example 3at a spinning speed of 4800 m/min. were subjected to heat treatment bypassing through a heating device for heat treatment whose internalsurface temperature was adjusted at 250° C. for 1.2 seconds at anextension ratio as shown in Table 6 without any contact with the surfaceof the heating device. The dynamic viscoelastic properties, mechanicaland thermal properties and degree of dye exhaustion of the fibers thusobtained are shown in Table 6.

From Table 6 it can be understood that the polyethylene terephthalatefibers heat-treated according to this invention are rendered easilydyeable and have fully satisfactory mechanical and thermal properties.

                                      TABLE 6                                     __________________________________________________________________________                              Mechanical & Thermal Properties                                                                        Degree                     Extension                                                                              Dynamic Viscoelastic Properties                                                                           Shrinkage in  of Dye                     Run                                                                              Ratio T.sub.max                                                                        (tan δ).sub.max                                                               tan δ.sub.220                                                                E'.sub.30                                                                        Tenacity                                                                           Elongation                                                                          Boiling Water Exhaustion                 No.                                                                              (%)   (°C.)                                                                     (-)   (-)  (g/d)                                                                            (g/d)                                                                              (%)   (%)     E'.sub.220 /E'.sub.150                                                              (%)                        __________________________________________________________________________    1*.sup.1                                                                         -30   101                                                                              0.238 0.056                                                                              45 2.9  82    1.1     0.67  68                         2  -15   104                                                                              0.214 0.055                                                                              71 3.2  78    1.5     0.75  82                         3  -5    105                                                                              0.195 0.049                                                                              80 3.3  52    2.4     0.76  94                         4  0     107                                                                              0.190 0.045                                                                              83 3.4  47    2.4     0.79  93                         5  +4    109                                                                              0.183 0.042                                                                              85 3.5  30    3.2     0.81  85                         __________________________________________________________________________     *.sup.1 Fiber of Run No. 1 is outside the scope of this invention.       

EXAMPLE 7

Polyethylene terephthalate having an intrinsic viscosity [η] of 0.62dl/g was extruded from a nozzle having 36 fine holes 0.35 mm in diameterat a spinning temperature of 295° C. The filaments extruded were cooledand solidified with a stream of air at 20° C. supplied from thedirection of all the circumference of the fiber in the paralleldirection of the running filaments and then, after adding an oilingagent, the filaments were wound three times on a pair of take up rollers7 as shown in FIG. 2 whose surface velocity was shown in Table 7 andwhose surface temperature was adjusted at most at 35° C., and then thefilaments wound on the take up rollers 7 were subjected to heattreatment by five times winding the filaments on a pair of heatingrollers 12 as shown in FIG. 2 whose surface temperature was adjusted at250° C. and subsequently the filaments thus heat-treated were wound on awinding roller 13 as shown in FIG. 3 to give filaments of 75d/ 36f. Inthis heat treatment the extension ratio of the filaments between thetake up rollers 7 and the heating rollers 12 was controlled at 3% andthe extension ratio of the filaments between the heating rollers 12 andthe take up rollers 13 was controlled at 1%. The period of time in whichthe running filaments contacted with the heating rollers is also shownin Table 7.

The features of the fine structure and the properties of thepolyethylene terephthalate fiber thus obtained are shown in Table 7. Itis observed that the distribution of local refractive index tends tobecome unsymmetrical with increased spinning speeds. The fibers producedat a spinning speed of 5500 m/min. had a symmetrical distribution oflocal refractive index.

                  TABLE 7                                                         ______________________________________                                                        Run No.                                                                       1*.sup.(1)                                                                           2       3                                              ______________________________________                                        Spinning Speed (m/min.)                                                                         3000     4500    5500                                       Period of Time for Heat                                                                         0.09     0.06    0.05                                       Treatment (second)                                                            Dynamic T.sub.max (°C.)                                                                      92       97    96                                       Visco-  (tan δ).sub.max (-)                                                                   0.322    0.203 0.181                                    elastic tan δ.sub.220 (-)                                                                     0.058    0.047 0.038                                            E'.sub.30 (g/d)                                                                             40       62    81                                       Mechanical                                                                            Tenacity (g/d)                                                                              2.3      3.5   3.7                                      & Thermal                                                                             Elongation (%)                                                                              81       58    51                                       Properties                                                                            Shrinkage in  30.3     4.0   3.1                                              Boiling Water (%)                                                             E'.sub.220 /E'.sub.150                                                                      0.63     0.70  0.71                                     Degree of Dye Exhaustion (%)                                                                    80       92      91                                         ______________________________________                                         *.sup.(1) Fiber of Run No. 1 is outside the scope of this invention.     

As is clear from Table 7, when polyethylene terephthalate is obtained ata spinning speed of 4500 m/min. or 5500 m/min. and then heat-treated byusing a pair of heating rollers which are conventionally employed in aspin-drawing machine, the present invention can be conducted in one stepwhere the spinning and the subsequent heat treatment are continuouslycombined.

EXAMPLE 8

The multifilaments prepared by the same procedures as in Example 2 at aspinning speed of 3000 m/min. and 4000 m/min. were subjected to heattreatment by using an apparatus for heat treatment as shown in FIG. 1 at250° C. for 0.9 second at -1% extension. Then the multifilaments thusheat-treated were subjected to drawing by a draw twister at a drawingtemperature of 100° C. at a draw ratio of 1.1.

The properties of the polyethylene terephthalate fibers before or afterstretching are shown in Table 8.

                  TABLE 8                                                         ______________________________________                                        Spinning Speed (m/min.)                                                                        3000        4000                                             Drawing          no      yes     no    yes                                    Dynamic  T.sub.max (°C.)                                                                    90      91    98    98                                   Visco-   (tan δ).sub.max (-)                                                                 0.320   0.301 0.214 0.212                                elastic  tan δ.sub.220 (-)                                                                   0.063   0.060 0.044 0.043                                Properties                                                                             E'.sub.30 (g/d)                                                                           39      45    58    70                                   Mechanical                                                                             Tenacity (g/d)                                                                            2.1     2.4   3.4   3.8                                  Properties                                                                             Elongation (%)                                                                            83      70    60    48                                   Degree of Dye Exhaustion (%)                                                                   84      83      91    90                                     ______________________________________                                    

As is seen from Table 8, after drawing stretching, the fibers preparedat a spinning speed of 3000 m/min. and 4000 m/min. are increased intenacity and decreased in elongation. However, with the fibers preparedat a spinning speed of 3000 m/min., even if drawn after heat treatment,the E'₃₀ is less than 55 g/d, the tenacity is less than 3 g/d and theelongation is as much as 70%. Thus, these fibers are inadequate for usein forming clothing. In contrast to this, when the fiber prepared at aspinning speed of 4000 m/min. is heat-treated according to thisinvention and then drawn, the properties of the resulting fiber isfurther improved and in addition, the degree of dye exhaustion is highand the fiber is dyeable under normal pressure.

EXAMPLE 9

Polyethylene terephthalate having an intrinsic viscosity [η] of 0.63dl/g was extruded from a nozzle having 7 fine holes 0.35 mm in diameterat a spinning temperature of 300° C. The filaments extruded were cooledand solidified with a stream of air at 22° C. supplied from thedirection of all the circumference of the fiber in the paralleldirection of the running filaments and then, after adding an oilingagent, the filaments were wound at a spinning speed of 4000 m/min. to9000 m/min. to give multifilaments of 35d/7f. Subsequently the woundmultifilaments were subjected to heat treatment by passing the filamentsthrough a heating cylinder 14 in an apparatus for wet heat treatment asshown in FIG. 3 where superheated steam of 239° C. was jetted throughslits 15, for 0.6 second at 1% extension. In the heating cylinder 14 themol fraction of H₂ O was 36%.

The features of the fine structure and properties of the polyethyleneterephthalate fiber thus obtained are shown in Table 9.

As a reference, the fiber of 35d/7f having been obtained at a spinningspeed of 3000 m/min. and the fiber of 35d/7f having been obtained at aspinning speed of 1500 m/min. and then drawn at 130° C. at a draw ratioof 3.3 were subjected to the same wet heat treatment as described above.The properties of these fibers are also shown in Table 9.

From Table 9 it can be understood that the fibers having been obtainedat a spinning speed of at least 4000 m/min. and then wet heat-treated at238° C. for 0.6 second at 1% extension are rendered easily dyeable andare excellent in color fastness and fully satisfactory in mechanicalproperties and thermal stability. In contrast, the fiber having beenobtained at a spinning speed of 3000 m/min. and then wet heat-treatedunder the above described conditions is rendered easily dyeable but ispoor in mechanical properties, and the fiber having been obtained at aspinning speed of 1500 m/min., drawn at a draw ratio of 3.3 and then wetheat-treated under the above described conditions is not rendered easilydyeable.

                                      TABLE 9                                     __________________________________________________________________________                                    Refractive Index                              Spinning      Dynamic Viscoelastic Properties                                                                          Distribution                         Run Speed                                                                              Draw T.sub.max                                                                         (tan δ).sub.max                                                               tan δ.sub.220                                                                E'.sub.30                                                                        Δn                                                                           n∥(0)                                                                    of Local T.sub.min *.sup.(3)                                                               T.sub.m3 *.sup.(3)      No. (m/min.)                                                                           Ratio*.sup.(1)                                                                     (°C.)                                                                      (-)   (-)  (g/d)                                                                            (×10.sup.-3)                                                                 (-) Refractive Index                                                                       (°C.)                                                                      (°C.)            __________________________________________________________________________    1   9000 --   99  0.145 0.020                                                                              73 115  1.701                                                                             symmetry 226 298                     2   8000 --   96  0.147 0.022                                                                              72 121  1.695                                                                             "        224 296                     3   7000 --   92  0.154 0.025                                                                              74 115  1.694                                                                             "        221 292                     4   6000 --   94  0.170 0.032                                                                              75  92  1.682                                                                             "        215 289                     5   5000 --   95  0.208 0.045                                                                              76  63  1.671                                                                             "        214 284                     6   4000 --   100 0.222 0.051                                                                              59  36  1.650                                                                             "        212 285                     7*.sup.(2)                                                                        3000 --   90  0.320 0.060                                                                              37 175  1.602                                                                             "        201 288                     8*.sup.(2)                                                                        1500 3.3  133 0.103 0.039                                                                              87      1.692                                                                             unsymmetry                                                                             211 293                     __________________________________________________________________________                Mechanical & Thermal Properties                                                                        Degree                                   Crystal Structure      Shrinkage in  of Dye                                   Run                                                                              Xc ACS                                                                              CO Tenacity                                                                           Elongation                                                                          Boiling Water Exhaustion                                                                          Color Fastness                     No.                                                                              (%)                                                                              (Å)                                                                          (%)                                                                              (%)  (%)   (%)     E'.sub.220 /E'.sub.150                                                              (%)   Light                                                                             Rubbing                                                                            Sublimation               __________________________________________________________________________    1  78 76 92 3.7  28    1.4     0.80  92    5   5    4˜5                 2  76 64 93 3.9  30    1.5     0.78  91    5   5    4˜5                 3  75 59 92 4.2  39    2.0     0.74  91    5   5    4                         4  69 55 90 4.1  46    2.5     0.74  90    5   4˜5                                                                          4                         5  53 52 88 3.8  55    3.0     0.71  88    5   5    4                         6  41 44 84 3.6  60    4.1     0.69  85    5   5    4                         7*.sup.(2)                                                                       29 25 50 2.7  85    29.0    0.65  81    4˜5                                                                         5    4                         8*.sup.(2)                                                                       62 18 87 4.9  29    6.9     0.55  42    3   5    4˜5                 __________________________________________________________________________     *.sup.(1) Draw ratio at 130° C.                                        *.sup.(2) Fibers of Run Nos. 7 and 8 are outside the scope of this            invention.                                                                    *.sup.(3) T.sub.min and T.sub.m3 are values before the heat treatment.   

EXAMPLE 10

Polyethylene terephthalate having an intrinsic viscosity [η] of 0.64dl/g was extruded from a nozzle having 600 fine holes 0.3 mm in diameterat a spinning temperature of 298° C. The filaments extruded were cooledand solidified with a stream of air at 20° C. supplied from thedirection of all the circumference of the fiber in the paralleldirection of the running filaments and then, after adding an oilingagent, the filaments were wound at a spinning speed of 4000 m/min. to9000 m/min. to give a fiber bundle of 1800d/600f. Then 100 of the fiberbundle was bundled to give a tow of 180,000d/60,000f and the tow wassubjected to wet heat treatment by passing the tow through an apparatusfor wet heat treatment as shown in FIG. 4 at 2% extension for 0.9 secondusing superheated steam of 238° C. where the mol fraction of H₂ O was40%.

The features of the fine structure and properties of the polyethyleneterephthalate tow thus obtained are shown in Table 10.

As a reference, the tow of 180,000d/60,000f having been obtained at aspinning speed of 3000 m/min. and the tow of 180,000d/60,000f havingbeen obtained at a spinning speed of 1500 m/min. and then drawn at 130°C. at a draw ratio of 3.3 were subjected to the same wet heat treatmentas described above. The properties of these tows are also shown in Table10.

From Table 10 it can be understood that the tows having been obtained ata spinning speed of at least 4000 m/min. and then wet heat-treated at238° C. for 0.9 second at 2% extension are rendered easily dyeable andare excellent in color fastness and fully satisfactory in mechanicalproperties and thermal stability. In contrast, the tow having beenobtained at a spinning speed of 3000 m/min. and then wet heat-treatedunder the above described conditions is rendered easily dyeable but thegrowth of crystals is not sufficient and the thermal stability of finestructure and the mechanical properties are poor, and the tow havingbeen obtained at a spinning speed of 1500 m/min., drawn at a draw ratioof 3.3 and then wet heat-treated under the above described conditions isnot rendered easily dyeable.

                                      TABLE 10                                    __________________________________________________________________________    Spinning      Dynamic Viscoelastic Properties                                                                         Crystal Structure                     Run Speed                                                                              Draw T.sub.max                                                                         (tan δ).sub.max                                                               tan δ.sub.220                                                                 E'.sub.30                                                                         T.sub.min                                                                        T.sub.m3                                                                         X.sub.c                                                                           ACS                                                                             CO                              No. (m/min.)                                                                           Ratio*.sup.(1)                                                                     (°C.)                                                                      (-)   (-)   (g/d)                                                                             (°C.)                                                                     (°C.)                                                                     (%) (Å)                                                                         (%)                             __________________________________________________________________________    1   9000 --   98  0.143 0.019 75  227                                                                              297                                                                              79  74                                                                              93                              2   8000 --   96  0.146 0.021 74  223                                                                              296                                                                              75  63                                                                              93                              3   7000 --   93  0.153 0.024 76  220                                                                              292                                                                              74  57                                                                              91                              4   6000 --   93  0.171 0.031 77  214                                                                              289                                                                              68  53                                                                              89                              5   5000 --   94  0.206 0.046 75  213                                                                              284                                                                              51  50                                                                              87                              6   4000 --   98  0.215 0.053 56  212                                                                              284                                                                              42  44                                                                              82                              7*.sup.(2)                                                                        3000 --   91  0.321 0.058 34  200                                                                              287                                                                              27  24                                                                              48                              8*.sup.(2)                                                                        1500 3.3  132 0.105 0.038 85  210                                                                              292                                                                              61  17                                                                              87                              __________________________________________________________________________    Mechanical & Thermal Properties                                                                           Degree                                                          Shrinkage in  of Dye                                            Run                                                                              Tenacity                                                                           Elongation                                                                          Boiling Water Exhaution                                                                           Color Fastness                              No.                                                                              (g/d)                                                                              (%)   (%)     E'.sub.220 /E'.sub.150                                                              (%)   Light                                                                             Rubbing                                                                            Sublimation                        __________________________________________________________________________    1  3.6  27    1.5     0.81  93    5   5    4˜5                          2  3.8  29    1.7     0.78  92    5   5    4˜5                          3  3.9  38    2.2     0.75  91    5   5    4                                  4  3.7  49    2.6     0.74  91    5   5    4                                  5  3.5  52    3.5     0.70  89    5   4˜5                                                                          4˜5                          6  3.3  61    4.3     0.68  86    5   5    4                                  7*.sup.(2)                                                                       2.2  88    30.5    0.64  81    4˜5                                                                         5    4                                  8*.sup.(2)                                                                       4.7  30    6.9     0.54  43    3   5    4˜5                          __________________________________________________________________________     *.sup.(1) Draw ratio at 130° C.                                        *.sup.(2) Fibers of Run Nos. 7 and 8 are outside the scope of this            invention.                                                               

EXAMPLE 11

The tow of 180,000d/60,000f having a T_(min) of 212° C. and aT_(m).spsb.3 of 284° C. prepared by the same procedures as in Example 2at a spinning speed of 4000 m/min. was subjected to wet heat treatmentby using an apparatus for wet heat treatment as shown in FIG. 3 in whichsuperheated steam of a temperature as shown in Table 11 was employed,for 0.7 second at -4% extension. In this wet heat treatment the molfraction of H₂ O was 45%. The dynamic viscoelastic properties,mechanical and thermal properties and degree of dye exhaustion ratio ofthe tow thus obtained are shown in Table 11.

From Table 11 it can be understood that the tows wet heat-treatedaccording to this invention are rendered easily dyeable and have fullysatisfactory mechanical and thermal properties.

                                      TABLE 11                                    __________________________________________________________________________    Wet Heat                   Mechanical & Thermal Properties                                                                        Degree                    Treament  Dynamic Viscoelastic Properties                                                                           Shrinkage in  of Dye                    Run                                                                              Temperature                                                                          T.sub.max                                                                        (tan δ).sub.max                                                               tan δ.sub.220                                                                E'.sub.30                                                                        Tenacity                                                                           Elongation                                                                          Boiling Water Exhaustion                No.                                                                              (°C.)                                                                         (°C.)                                                                     (-)   (-)  (g/d)                                                                            (g/d)                                                                              (%)   (%)     E'.sub.220 /E'.sub.150                                                              (%)                       __________________________________________________________________________    1*.sup.(1)                                                                       215    121                                                                              0.149 0.044                                                                              64 3.7  79    9.0     0.64  41                        2  225    98 0.171 0.043                                                                              76 3.8  59    3.1     0.68  91                        3  230    97 0.214 0.042                                                                              71 3.8  51    2.2     0.74  92                        4  235    92 0.245 0.050                                                                              71 3.7  44    1.4     0.67  91                        5*.sup.(2)                                                                       --     130                                                                              0.194 0.048                                                                              61 3.6  82    13.0    0.64  59                        __________________________________________________________________________     *.sup.(1) Tow of Run No. 1 is outside the scope of this invention.            *.sup.(2) Tow without wet heat treatment.                                

EXAMPLE 12

The multifilaments of 35d/7f having a T_(min) of 213° C. and aT_(m).spsb.3 of 283° C. prepared by the same procedures as in Example 2at a spinning speed of 4500 m/min. were subjected to wet heat treatmentby using an apparatus for wet heat treatment as shown in FIG. 3 wheresuperheated steam of 225° C. was employed, for 0.7 second at anextension ratio as shown in Table 12. In this wet heat treatment the molfraction of H₂ O was 57%. The dynamic viscoelastic properties,mechanical and thermal properties and degree of dye exhaustion of thefiber thus obtained are shown in Table 12.

From Table 12 it can be understood that the polyethylene terephthalatefibers heat-treated according to this invention are rendered easilydyeable and at -30% extension the initial modulus E'₃₀ tends to decreaseand also at +6% extension the degree of dye exhaustion tends todecrease.

                                      TABLE 12                                    __________________________________________________________________________                              Mechanical & Thermal Properties                                                                        Degree                     Extension                                                                              Dynamic Viscoelastic Properties                                                                           Shrinkage in  of Dye                     Run                                                                              Ratio T.sub.max                                                                        (tan δ).sub.max                                                               tan δ.sub.220                                                                E'.sub.30                                                                        Tenacity                                                                           Elongation                                                                          Boiling Water Exhaustion                 No.                                                                              (%)   (°C.)                                                                     (-)   (-)  (g/d)                                                                            (g/d)                                                                              (%)   (%)     E'.sub.220 /E'.sub.150                                                              (%)                        __________________________________________________________________________    1*.sup.(1)                                                                       -30   101                                                                              0.240 0.054                                                                              47 2.9  75    1.1     0.68  92                         2  -15   104                                                                              0.213 0.053                                                                              71 3.4  68    1.5     0.73  90                         3    0   106                                                                              0.196 0.048                                                                              82 3.5  51    2.0     0.75  93                         4   +4   108                                                                              0.192 0.047                                                                              84 3.6  45    2.4     0.77  92                         5   +6   111                                                                              0.121 0.041                                                                              87 3.9  27    3.3     0.80  72                         __________________________________________________________________________     *.sup.(1) Fiber of Run No. 1 is outside the scope of this invention.     

EXAMPLE 13

Polyethylene terephthalate having a [η] of 0.62 dl/g was extruded from anozzle having 36 fine holes 0.35 mm in diameter at a spinningtemperature of 300° C. The filaments extruded were cooled and solidifiedwith a stream of air at 20° C. supplied from the direction of all thecircumference of the fiber in the parallel direction of the runningfilaments and then, after adding an oiling agent, the filaments werewound three times on a take up roller 7 as shown in FIG. 3 whose surfacevelocity was shown in Table 13 and whose surface temperature wasadjusted at most at 35° C., and then the filaments wound were subjectedto wet heat treatment by passing the filaments through a heatingcylinder for heat treatment 14 as shown in FIG. 3 using superheatedsteam of 235° C. where the mol fraction of H₂ O was 50%. The filamentsthus wet heat-treated were wound three times on a pair of deriveryrollers 21 as shown in FIG. 3 and subsequently wound on a winding roller22 as shown in FIG. 3 to give filaments of 75d/36f. In this wet heattreatment the extension ratio of the filaments between the take-uproller 7 and the derivery rollers 21 was controlled at 0.5%. The periodof time for wet heat treatment of the filaments, i.e., the period oftime in which the filaments were passed through the heating cylinder 14,i.e., the surface velocity of the take-up rollers 7 is also shown inTable 13.

                  TABLE 13                                                        ______________________________________                                                        Run No.                                                                       1*.sup.(1)                                                                           2       3                                              ______________________________________                                        Spinning Speed (m/min.)                                                                         3000     4500    5500                                       Period of Time for Wet                                                                          0.09     0.06    0.05                                       Heat Treatment (second)                                                       Dynamic  T.sub.max (°C.)                                                                     93       98    97                                       Visco-   (tan δ).sub.max (-)                                                                  0.323    0.205 0.192                                    elastic  tanδ.sub.220 (-)                                                                     0.060    0.048 0.040                                    Properties                                                                             E'.sub.30 (g/d)                                                                            39       63    80                                       Mechanical                                                                             Tenacity (g/d)                                                                             2.4      3.8   4.0                                      & Thermal                                                                              Elongation (%)                                                                             82       57    51                                       Properties                                                                             Shrinkage in 29.8     4.1   2.7                                               Boiling Water (%)                                                             E'.sub.220 / E'.sub.150                                                                    0.63     0.71  0.72                                     Degree of Dye Exhaustion (%)                                                                    80       92      91                                         ______________________________________                                         *.sup.(1) Fiber of Run No. 1 is outside the scope of this invention.     

As is clear from Table 13, when the present invention is conducted byspinning polyethylene terephthalate at a spinning speed of 4500 m/min.or 5500 m/min. and continuously, i.e., without winding, subjecting thefilaments to wet heat treatment, i.e., by continuously combining thespinning step with the subsequent heat treatment step, the filamentsobtained can be rendered easily dyeable.

EXAMPLE 14

The polyethylene terephthalate filaments of 1800d/600f having a T_(min)of 212° C. and T_(m).spsb.3 of 281° C. prepared at a spinning speed of4000 m/min. by the same procedures as in Example 10 were subjected tocrimping without wet heat treatment at a temperature of 180° C. orhigher and cut into a staple fiber having a length of 76 mm. The staplefiber obtained was stuffed into cans having a number of holes at theirside wall at an apparent specific gravity of 2 Kg/m³ and the cans wereplaced in an autoclave. After the air inside the autoclave was deaeratedto a reduced pressure of 15 mmHg by a vacuum pump, superheated steam of224° C. was blown into the autoclave for one minute, and then the steaminside the autoclave was withdrawn under reduced pressure, and againsuperheated steam of 224° C. was blown into the autoclave for one minuteand the fiber was taken out of the autoclave.

The properties of the polyethylene terephthalate fibers before and afterwet heat treatment are shown in Table 14.

As is clear from Table 14, the E'₃₀ and the tenacity with the fiber notwet heat-treated are low and at the same time, the degree of dyeexhaustion is low. On the other hand, the fiber wet heat-treatedaccording to this invention has mechanical properties sufficient forpractical purposes such as an E'₃₀ of more than 55 g/d, a tenacity ofmore than 3 g/d, an elongation of less than 60% and a degree of dyeexhaustion of more than 80%, and is rendered dyeable under normalpressure.

                  TABLE 14                                                        ______________________________________                                        Wet Heat Treatment   no      yes                                              Dynamic    T.sub.max (°C.)                                                                      108     104                                          Visco-     (tan δ).sub.max (-)                                                                   0.290   0.211                                        elastic    tan δ.sub.220 (-)                                                                     0.062   0.030                                        Properties E'.sub.30 (g/d)                                                                             34      59                                           Mechanical Tenacity (g/d)                                                                              2.7     3.2                                          Properties Elongation (%)                                                                              82      53                                           Degree of Dye Exhaustion (%)                                                                       65      86                                               ______________________________________                                    

EXAMPLE 15

The staple fiber before wet heat treatment as obtained in Example 14 wasopened in carding to give a sliver and the sliver was stuffed into thesame cans as in Example 14 at an apparent specific gravity of 1.5 Kg/m³and was subjected to the same wet heat treatment as in Example 14.

The properties of the polyethylene terephthalate fibers before and afterwet heat treatment are shown in Table 15.

As is clear from Table 15, the E'₃₀, the tenacity and the degree of dyeexhaustion of the fiber not wet heat-treated are low. On the other hand,the fiber wet heat-treated according to this invention has mechanicalproperties sufficient for practical purposes such as an E'₃₀ of morethan 55 g/d, a tenacity of more than 3 g/d, an elongation of less than60% and a degree of dye exhaustion of more than 80%, and is rendereddyeable under normal pressure.

                  TABLE 15                                                        ______________________________________                                        Wet Heat Treatment   no      yes                                              Dynamic    T.sub.max (°C.)                                                                      110     103                                          Visco-     (tan δ).sub.max (-)                                                                   0.280   0.212                                        elastic    tan δ.sub.220 (-)                                                                     0.061   0.047                                        Properties E'.sub.30 (g/d)                                                                             34      60                                           Mechanical Tenacity (g/d)                                                                              2.7     3.2                                          Properties Elongation (%)                                                                              81      51                                           Degree of Dye Exhaustion (%)                                                                       64      87                                               ______________________________________                                    

EXAMPLE 16

The staple fiber before wet heat treatment as obtained in Example 14 wasspun into a spun yarn having a metric count of 40 by the conventionalmethod. This spun yarn was subjected to wet heat treatment by passingthe spun yarn through a heating cylinder for heat treatment 14 as shownin FIG. 3 using superheated steam of 230° C. for 1.5 seconds at 1%extension. In this wet heat treatment the mol fraction of H₂ O was 60%.The degree of dye exhaustion before and after wet heat treatment wasmeasured and found to be 64% and 88%, respectively.

EXAMPLE 17

Polyethylene terephthalate having a [η] of 0.62 dl/g was extruded from anozzle having 600 fine holes 0.35 mm in diameter at a spinningtemperature of 300° C. The filament extruded were cooled and solidifiedwith a stream of air at 21° C. supplied from the direction of all thecircumference of the fiber in the parallel direction of the runningfilaments and then, after adding an oiling agent, the filaments werewound at a spinning speed of 4000 m/min. to 9000 m/min. to give a fiberbundle of 1800d/600f. Subsequently the fiber bundle thus obtained weresubjected to heat treatment by passing the fiber bundle through a heaterfor heat treatment 9 as shown in FIG. 1 whose internal temperature wasadjusted at 244° C. for 0.9 second at 0% extension without any contractwith the surface of the heater.

The features of the fine structure and properties of the polyethyleneterephthalate fiber bundle thus obtained are shown in Table 16.

As a reference, the fiber bundle of 1800d/600f having been obtained at aspinning speed of 3000 m/min. and the fiber bundle of 1800d/600f havingbeen obtained at a spinning speed of 1000 m/min. and then drawn at 130°C. at a draw ratio of 3.3 were subjected to the same heat treatment asdescribed above. The properties of these fiber bundles are also shown inTable 16.

From Table 16 it can be understood that the fiber bundle having beenobtained at a spinning speed of 4000 m/min. or more and thenheat-treated at 244° C. for 0.9 second at 0% extension are renderedeasily dyeable and are fully satisfactory in mechanical properties andthermal stability as the starting material for spinning. In contrast,the fiber bundle having been obtained at a spinning speed of 3000 m/min.and then heat-treated under the above described conditions and the fiberbundle having been obtained at a spinning speed of 1000 m/min., drawn ata draw ratio of 3.3 and then heat-treated under the above describedconditions are not satisfactory in the above described properties.

                                      TABLE 16                                    __________________________________________________________________________    Spinning      Dynamic Viscoelastic Properties                                                                        Crystal Structure                      Run Speed                                                                              Draw T.sub.max                                                                         (tan δ).sub.max                                                               tan δ.sub.220                                                                E'.sub.30                                                                         T.sub.min                                                                        T.sub.m3                                                                         X.sub.c                                                                           ACS                                                                              CO                              No. (m/min.)                                                                           Ratio*.sup.(1)                                                                     (°C.)                                                                      (-)   (-)  (g/d)                                                                             (°C.)                                                                     (°C.)                                                                     (%) (Å)                                                                          (%)                             __________________________________________________________________________    1   9000 --   97  0.145 0.018                                                                              74  229                                                                              298                                                                              80  77 93                              2   8000 --   95  0.147 0.019                                                                              75  225                                                                              296                                                                              79  66 92                              3   7000 --   92  0.154 0.021                                                                              78  221                                                                              293                                                                              75  59 92                              4   6000 --   93  0.172 0.030                                                                              81  215                                                                              290                                                                              69  55 91                              5   5000 --   95  0.200 0.044                                                                              80  214                                                                              285                                                                              54  52 88                              6   4000 --   98  0.209 0.050                                                                              59  213                                                                              284                                                                              33  45 84                              7*.sup.(2)                                                                        3000 --   90  0.311 0.060                                                                              38  201                                                                              287                                                                              27  24 50                              8*.sup.(2)                                                                        1000 3.3  132 0.102 0.035                                                                              89  211                                                                              291                                                                              59  20 88                              __________________________________________________________________________    Mechanical & Thermal Properties                                                                           Degree                                                          Shrinkage in  of Dye                                            Run                                                                              Tenacity                                                                           Elongation                                                                          Boiling Water Exhaustion                                                                          Color Fastness                              No.                                                                              (g/d)                                                                              (%)   (%)     E'.sub.220 /E'.sub.150                                                              (%)   Light                                                                             Rubbing                                                                            Sublimation                        __________________________________________________________________________    1  3.6  28    1.3     0.81  93    4˜5                                                                         5    4                                  2  3.9  31    1.4     0.79  93    4˜5                                                                         5    4                                  3  4.3  39    1.9     0.76  92    4˜5                                                                         5    4                                  4  4.1  44    1.9     0.74  92    4˜5                                                                         5    4                                  5  3.7  52    2.0     0.72  91    4˜5                                                                         5    4                                  6  3.5  58    2.5     0.71  92    4˜5                                                                         4˜5                                                                          4                                  7*.sup.(2)                                                                       2.2  89    30.2    0.65  83    4˜5                                                                         5    3                                  8*.sup.(2)                                                                       4.5  30    4.5     0.55  44    3   4˜5                                                                          4˜5                          __________________________________________________________________________     *.sup.(1) Draw ratio at 130° C.                                        *.sup.(2) Fibers of Run Nos. 7 and 8 are outside the scope of this            invention.                                                               

EXAMPLE 18

Polyethylene terephthalate having a [η] of 0.64 dl/g was obtained at aspinning speed of 4500 m/min. in the same manner as in Example 17 togive a fiber bundle of 1800d/600f. Then 100 of the fiber bundle wasbundled to give a tow of 180,000d/60,000f, and the tow was made flat bya comb-shaped guide and subjected to heat treatment by passing the towthrough a heater for heat treatment 9 as shown in FIG. 1 whose internaltemperature was adjusted at 250° C. for 1 second at -4% extension. Theproperties of the polyethylene terephthalate fiber bundle before andafter heat treatment are shown in Table 17.

                  TABLE 17                                                        ______________________________________                                                           After     Before                                                              Heat      Heat                                             Properties         Treatment Treatment                                        ______________________________________                                        Dynamic T.sub.max (°C.)                                                                       96        113                                          Visco-  (tan δ).sub.max (-)                                                                    0.204     0.247                                        elastic tan δ.sub.220 (-)                                                                      0.039     0.061                                        Properties                                                                            E'.sub.30 (g/d)                                                                              79.2      46.5                                         Mechanical                                                                            Tenacity (g/d) 3.9       3.5                                          & Thermal                                                                             Elongation (%) 49        80                                           Properties                                                                            Shrinkage in   1.7       7.9                                                  Boiling Water (%)                                                     Degree of Dye Exhaustion (%)                                                                     92.8      65.8                                             ______________________________________                                    

From Table 17 it can be understood that the tow after heat treatment isremarkably rendered easily dyeable and, as a result, dyeable undernormal pressure. Also the mechanical properties of the tow aresufficient as a starting material for spinning.

EXAMPLE 19

Polyethylene terephthalate having a [η] of 0.63 dl/g was extruded from anozzle having 600 fine holes 0.30 mm in diameter at a spinningtemperature of 302° C. The filaments extruded were cooled and solidifiedwith a stream of air at 20° C. supplied from the direction of all thecircumference of the fiber in the parallel direction of the runningfilaments and then, after adding an oiling agent, the filaments werewound at a spinning speed of 5500 m/min. to give a fiber bundle of900d/600f. Subsequently 200 of the fiber bundles thus obtained werebundled to give a tow of 180,000d. This tow was subjected to crimping byusing a stuffer box by the conventional method and then cut with Gru-Grucutter at a length of 36 mm to give a staple fiber. Then a spun yarn ofa cotton count of 50 was produced by blending on a drawing frameaccording to the conventional method in such a manner that the weightratio of the polyethylene terephthalate staple fiber to cotton fiberhaving an average length of 25.4 mm was 65:35. The blended yarn thusobtained was subjected to heat treatment by passing the blended yarnthrough an apparatus for dry heat treatment 14 as shown in Table 3 whoseinternal temperature was adjusted at 235° C. for one second at an 0.5%extension without any contact with the surface of the apparatus. Theblended yarns before and after the heat treatment were immersed in aSchweitzer's reagent (i.e., a cuprammonium solution) to remove thecotton fiber by dissolution and the degree of dye exhaustion of thepolyethylene terephthalate fiber left was measured. As a result, thedegree of dye exhaustion of the fiber before the heat treatment was 65%while that after the heat treatment was remarkably improved to 89%.

EXAMPLE 20

Polyethylene terephthalate having a [η] of 0.63 dl/g was extruded from anozzle having 7 fine holes 0.35 mm in diameter at a spinning temperatureof 300° C. The filament extruded were cooled and solidified with astream of air at 22° C. supplied from the direction of all thecircumference of the fiber in the parallel direction of all the runningfilaments and then, after adding an oiling agent, the filaments werewound at a spinning speed of 3000 m/min. to 9000 m/min. to givemultifilaments of 35d/7f. Subsequently the multifilaments thus obtainedwere subjected to heat treatment by passing the multifilaments through aheater for heat treatment 9 as shown in FIG. 1 whose internaltemperature was adjusted at 250° C.±0.5° C. for 0.6 second at -2%extension without any contract with the surface of the heater.

Then the multifilaments was subjected to false twisting by using anapparatus for false twisting as shown in FIG. 5 under the followingconditions:

    ______________________________________                                        First heater              35                                                  Length                    1 m                                                 Temperature               200° C.                                      Stabilizing heater        38                                                  Diameter                  4 m/m φ                                         Length                    0.6 m                                               Temperature               190° C.                                      Ratio of surface speeds of rollers 37 to rollers 34,                                                    1.125                                               i.e., draw ratio                                                              Number of twists          3500 t/m                                            Linear velocity of rollers 37                                                                           146 m/min.                                          Take-up ratio             4.3%                                                Stabilized feed ratio     16%                                                 ______________________________________                                    

The features of the fine structure and properties of the false twistedpolyethylene terephthalate fiber are shown in Table 18.

The false twisted fiber of Run No. 1 has an E'₃₀ as low as 40 g/d, poordimensional stability and excessively high elongation. In addition, thedegree of dye exhaustion is 68% and it cannot be said that fiber isdyeable under normal pressure. The degree of dye exhaustion of 80%approximately corresponds to the dyeing at 130° C. at a pressure higherthan atmospheric pressure. Accordingly, the false twisted fibers of thisinvention having a degree of dye exhaustion of at least 80% are dyeableunder normal pressure.

                                      TABLE 18                                    __________________________________________________________________________    Spinning   Dynamic Viscoelastic Properties                                                                    Crystal Structure                             Run   Speed                                                                              T.sub.max                                                                          (tan δ).sub.max                                                               tan δ.sub.220                                                                  E'.sub.30                                                                        X.sub.c                                                                            ACS                                                                              CO                                    No.   (m/min.)                                                                           (°C.)                                                                       (-)   (-)    (g/d)                                                                            (%)  (Å)                                                                          (%)                                   __________________________________________________________________________    1*.sup.(1)                                                                          3000 120  0.14  0.035  40 35   32 46                                    2     4000  98  0.25  0.025  58 42   45 84                                    3     5000 102  0.16  0.024  65 71   52 86                                    4     6000 105  0.18  0.024  70 76   56 91                                    5     7000 105  0.17  0.023  74 80   62 94                                    6     8000 104  0.159 0.021  78 82   66 95                                    7     9000  98  0.145 0.020  80 84   70 95                                    __________________________________________________________________________    Mechanical & Thermal Properties                                                                        Degree                                                             Crimp      of Dye                                               Run                                                                              Tenacity                                                                           Elongation                                                                          Retention  Exhaustion                                                                          Color Fastness                                 No.                                                                              (g/d)                                                                              (%)   (%)  E'.sub.220 /E'.sub.150                                                              (%)   Light                                                                             Rubbing                                                                            Sublimation                           __________________________________________________________________________    1*.sup.(1)                                                                       2.4  71    42   0.68  68    4˜5                                                                         5    3                                     2  3.7  58    72   0.72  84    4˜5                                                                         5    3˜4                             3  3.8  52    75   0.74  86    4˜5                                                                         5    4                                     4  4.1  45    78   0.75  86    4˜5                                                                         5    4                                     5  4.3  39    77   0.76  86    4˜5                                                                         5    4                                     6  4.3  38    74   0.77  94    4˜5                                                                         5    4                                     7  4.4  36    71   0.78  94    4˜5                                                                         5    4                                     __________________________________________________________________________     *.sup.(1) Fiber of Run No. 1 is outside of the scope of this invention.  

What is claimed is:
 1. A process for producing a fiber not undergoingfalse twisting and consisting essentially of polyethylene terephthalatecapable of being dyed under normal pressure and having an initialmodulus at 30° C. of about 55 g/d to about 130 g/d, a relationshipbetween a peak temperature (T_(max) (°C.)) at the peak of a dynamicmechanical loss tangent (tan δ) measured with a frequency of 110 Hz anda peak value of the dynamic mechanical loss tangent ((tan δ)_(max))represented by the formula:

    (tan δ).sub.max ≧1×10.sup.-2 (T.sub.max -105)

and a (tan δ)_(max) of about 0.14 to about 0.30, a dynamic mechanicalloss tangent at 220° C. (tan δ₂₂₀) of at most about 0.055, and a T_(max)(°C.) of at most about 105° C., which comprises subjecting apolyethylene terephthalate fiber obtained at a spinning speed of atleast about 4000 m/min. to heat treatment at a temperature ranging froma temperature at which a dynamic modulus (E') of the fiber deviates froma tangent line at 180° C. of a logarithm of the E' of thefiber-temperature curve (T_(min)) plus 10° C. to a temperature ofcompletion of melting (T_(m).spsb.3) at a melting curve of the fibermeasured by a differential scanning calorimeter (DSC) plus 10° C.
 2. Theprocess according to claim 1, wherein the heat treatment is conducted atan extension ratio of from about -20% to about +5%.
 3. The processaccording to claim 1, wherein the fiber spun is continuously subjectedto heat treatment at a temperature higher than T_(min) +20° C. in thespinning step without winding.
 4. The process according to claim 2,wherein the heat treatment is conducted at an extension ratio of fromabout -5% to about 0%.
 5. The process according to claim 1, wherein theheat treatment temperature is at least about 235° C.
 6. The processaccording to claim 1, wherein the spinning speed is about 6000 m/min. toabout 9000 m/min.
 7. The process according to claim 1, wherein thespinning speed is about 8000 m/min. to about 9000 m/min.
 8. The processaccording to claim 1, wherein the heat treatment period of time is atmost about 10 seconds.
 9. The process according to claim 1, wherein thefiber spun is subjected to heat treatment in a wet heat atmosphere at atemperature of at most 240° C.
 10. The process according to claim 9,wherein the wet heat atmosphere is superheated steam.
 11. The processaccording to claim 10, wherein the polyethylene terephthalate fiberobtained at a spinning speed of about 6000 m/min. to about 9000 m/min.is subjected to heat treatment in a wet heat atmosphere at a temperatureof at most about 235° C.
 12. The process according to claim 9, whereinthe polyethylene terephthalate fiber is spun at a spinning speed ofabout 8000 m/min. to about 9000 m/min., wound and subsequently subjectedto heat treatment in a wet heat atmosphere at a temperature of at most240° C.
 13. The process according to claim 9, wherein the wet heattreatment is conducted at an extension ratio of about -20% to about +5%.14. The process according to claim 13, wherein the extension ratio isabout -5% to about 0%.
 15. The process according to claim 3, wherein theheat treatment is conducted at an extension ratio of from about -5% toabout 0%.